Gaulish is one of the ancient languages preceding most Celcic languages, and was no longer spoken after 500. It was mainly spoken in what we know as Gaul (present-day France and Belgium. 
Below you can find a great lists of Gaulish words & meanings.

Sources:

1. Whatmough J.  The dialects of Ancient Gaul, Cambridge, 1970.
2. Kalygin, V. The Language of the ancient Irish poetry. Moscow, 1986.
3. Kalygin V., Korolev A. Introduction to the Celtic Philology. Moscow, 1989.
4. Lewis G., Pedersen H. Vergleichende Grammatik der keltischen Sprachen, Goettingen, 1909-13.
5. Mac-Bain, F. The etymological Dictionary of Celtic languages.
6. Fasmer, M. The etymological dictionary of the Russian language. Moscow, 1986.
Notes for Glossary:
a’, e’, i’, o’, u’ – long vowels: [a, e, i, o, u] respectively
CC – Common Celtic
OI – Old Irish
MI – Middle Irish
MB – Middle Breton
Glossary:

aballo- (an apple) [IE *amlu-, *samlu- ‘apple’?, OI uball]
adiat (aspiration)
aesus (m) (an age) [Latin aes, Irish aois]
allos (other, second) [IE *alyo-, OI aile]
ambi- (around)
ardus (high) [IE *er@d- ‘high’, CC *ardwo-]
are (before, at, on) [IE *par-, Greek para, Latin prae, OI ar]
arganto-, argento- (silver) [IE *arg’- ‘white, to shine’]
art- (a bear) [IE *arkt-, *Hart- ‘a bear’]
artuas (stone plates; pl.)
ater (m) (father) [IE *pa’te’r ‘a father’]
atespos (m) (an answer)
aus (an ear) [Latin ausus]
bagaudas (guerilla fighters) [OI ba’gaim ‘I fight’]
bardos (m) (a poet) [OI bard, Greek phrazo’ ‘I speak’]
beber, bibro- (a beaver) [IE *bebhro- ‘a wild animal, a beaver’]
beccus (a beak) [Old English becca ‘a hoe’, Middle High German bicke]
bedo- (a channel)
bekos (a bee) [IE *bhey- ‘a bee’, OI bech]
bel- (white; in Belenos, Belisama) [IE *bhel-, *bhal- ‘white, to shine’]
benn- (a top, a peak) [English knoll, Irish beann]
benna (a carriage) [OI buinne]
bitu- (world, life) [IE *gwei- ‘to live’, OI bith ‘world’]
boduus (m) (a raven) [OI bodb ‘raven’]
brace (malt) [IE *mar- ‘dirty’, OI mraich]
bratu- (to judge) [OI bra’th ‘court’]
briga (f) (a hill)
bri’ua (f) (a bridge) [Germanic *bro’wo’, *bruwwi’ ‘a bridge’, Old Church Slavonic brivno ‘a log’]
bru’kos (a pen)
caballos (m) (a working horse)
caddos (saint) [MI cád ‘holy’]
cambios (n) (exchange)
cambos (m) (a slope)
cammano- (a pitch, a step)
camulos (war god) [MI cuma ‘woe’, MB caffou ‘woe’]
candetum (a hundred feet long) [CC *cant-pedum, IE *ped- ‘a foot’]
cant- (an edge, a circle) [IE *kem- ‘to cover’, Welsh cant]
capt, coept (captured, taken; participle)
carb- (a wagon)
carros (m) (a wagon)
catu- (a battle) [IE *kot- ‘a battle’, Greek kotos ‘rage’, Middle High German hader ‘a quarrel’, OI cath ‘a battle’]
cauaros, cavarillus (a giant) [Welsh cawr, Cornish caur]
cervesia (f) (beer)
cet, cait (wood)
cingeto- (m) (a warrior) [OI cingim ‘I step, march’, cing ‘a warrior’, Welsh & Breton cam ‘a step’]
cintu-, cintus (first) [Latin recens ‘fresh, young’, Greek kainos ‘new’, Sanskrit kani’nas ‘young’, OI ce’t, ce’tna]
com- (with, together with) [Latin, Umbrian com-,cum-]
couer (appropriate, worth-while)
courmi (a sort of beer) [Latin cremor ‘dense juice’, Russian korm ‘forage’, OI coirm ‘beer’]
crix (curly)
crodio- (hard, difficult)
-cue, -pe (and) [IE *kwe ‘and’]
cumba (dishes)
dag- (kind)
decametos (tenth) [IE *dekmot ‘ten’]
dede (he put; 3rd sg. perf.) [IE *dhe’- ‘to put, to set’, OI dál]
delgu (I hold; 1st sg. pres.)
dervo- (a tree) [IE *deru- ‘a tree, wood’]
deus (m) (a god) [IE *deiwo- ‘a deity’]
dexs (right) [IE *deks- ‘right, correct’]
dibu e debu (to the gods and goddesses) [IE *deiwo- ‘a deity’]
divertomu (we turn; 1st pl. pres.) [IE *wer-t- ‘to turn, to roll’]
doenti (they give; 3st pl. pres. Celtiberian) [IE *do’- ‘to give’]
doro (a mouth) [IE *dhwer- ‘a door, a gate’]
drungus (m) (a crowd) [OI drong]
dubi- (black) [IE *dhubh- ‘to smoke’, OI dub ‘black’]
du’la- (a leaf) [MI duille, Welsh dalen, Middle Breton del]
dumno- (world) [OI domun ‘world’]
dunum (n) (a fort) [Germanic *tu’na- ‘town’]
dusios (a demon) [OI da’sacht ‘rage’]
eimu (we go; 1st pl. pres.) [IE *ei- ‘to go’]
embrekton (a dipped piece of food) [IE *mer- ‘wet’]
eporeto- (a chariot) [IE *ekwo- + *ret-]
epos, eqwos (a horse) [IE *ekwo- ‘a horse’]
es, ex (from, out of) [IE *eghs ‘out’, OI acht ‘but’]
esok- (a salmon) [Latin esox, Early Irish co’, Welsh, Breton eog, Welsh ehawc, Cornish ehog]
essedum (a two-seat wagon) [IE sed- ‘to sit’, OI saidim ‘I sit’]
gabi (take!; 2nd sg. imp.) [IE *gebh-, OI gabaim ‘I take’, Gothic giban ‘give’, Lithuanian gabe’nti ‘bring’]
gabro- (a goat) [OI gabor, Welsh gafr]
gaesum (n) (a spear)
geistl- (a lien)
gena (f) (a cheek)
geno-, gnatos (born) [IE *g’enu- ‘a knee, a kin, to know’, OI gnó]
giam- (a winter) [IE *gheim- ‘winter’]
glastu- (light blue) [Early Irish glass ‘pale’, Welsh, Old Welsh, Breton glas ‘green’, German glast ‘sheen’]
gobbo- (a mouth) [IE *gonbho- ‘a ledge’, Irish gob]
gutus (m) (a voice) [Irish guth]
inter (between) [IE *en-ter ‘between’]
iouin- (young) [IE *you-n- ‘young’]
isarno- (iron) [IE *esro-no- ‘red, bloody metal’?; or IE *ayos-, *ayes- ‘metal’]
landa- (a field) [IE *lendh- ‘open land’, OI land]
lanu- (flat, plain) [IE *plo-no- ‘full, plain, flat’]
lautro- (a bath) [Latin lavare ‘to wash’, OI lo’athar]
legasit (he laid), lega’ (laying; participle pres.) [OI lige ‘a bed’]
leux, lugus (light) [IE *leuk- ‘light, to shine’]
lexo- (a slope)
litano- (wide, broad) [IE *plotno- ‘wide’, OI lethan ‘wide’]
logan (a grave) [IE *legh- ‘to lie’]
luct- (a tribe, a part) [IE *leug- ‘to break’, OI lucht ‘a part’]
magus (young, a servant, a boy) [IE *maghu- ‘a young person’]
magu- (a field) [OI mag ‘field’]
maniakys (a neck bandage) [IE *moni’- ‘a neck’]
maponos (a son) [Ogham Irish maqq ‘a son’]
marka (a horse) [OI marc]
maru- (great) [IE *mar-, *mor- ‘great’]
marvos (dead) [IE *mer-, *mor- ‘to die’]
mat- (kind, good) [IE *ma- ‘good’, Irish ma’ith]
medios (medium) [IE *medhyo- ‘medium, middle’]
mesga (to mix) [IE *meik- ‘to mix’]
more-, -mori- (a sea) [Latin mare, OI muir, Slavic *more, Lithuanian marios]
naumetos (ninth) [IE *newno ‘nine’]
nemeton, nempton (a temple) [OI nemed ‘a temple’]
nertos (force, strength) [IE *@ner-, *ner-t- ‘strength, power’]
novio- (new) [IE *newo- ‘new’]
odocos (an elder) [Old Prussian addle ‘a fir’, Latin ebulus ‘elder’, Czech jedle ‘silver fir’]
ogros (cold) [IE *oug- ‘cold’, OI u’ar]
oinos (one) [IE *oino- ‘one’]
ollon (all, the whole) [MI oll ‘big’]
ouindho-, vindo- (white) [IE *weid- ‘to see’, OI find]
oxtometos (eighth) [IE *októ ‘eight’]
penno- (a head) [OI cenn, cend]
petri (four) [IE *kwetwores ‘four’]
petrudecametos (fourteenth)
petsi- (a thing)
pinpetos (fifth) [IE *penkwe ‘five’]
recto- (right) [IE *reg’- ‘to rule’, OI rigid]
re’da (a chariot) [IE *ret- ‘to run, to roll’, Irish ri’adaim ‘I ride’]
ritu- (a ford)
rix (pl. riges) (a king) [IE *reg’- ‘to rule’]
roudo- (red) [IE *reudh- ‘red, rust’, OI ruad]
sam- (a summer) [IE *sem- ‘summer’]
sapo- (soap)
sedlon (a saddle, a seat) [IE *sed- ‘to sit’, Slavic *sedlo ‘a saddle’]
sego- (a victory)
selua (a possession)
seno- (old) [IE *sen- ‘old’]
sirom (a star)
sistat (he stands, stays; 3st sg. pres. Celtiberian) [IE *sta’- ‘to stand’]
slug- (a servant) [Slavic *sluga ‘a servant’, Lithuanian slauga ‘service’, OI sluag ‘an army unit’]
smer- (fat) [Early Irish smir, Welsh mer, Old High German smero ‘grease’, Old English smeoru ‘lard’]
sosin (that)
suadu- (pleasant) [CC *sved- ‘sweet’, Latin suavis, English sweet]
suextos, sextos (sixth) [IE *sweks ‘six’]
tarvos (a bull) [IE *tauro- ‘a bull’]
tigern- (a house) [OI tech]
teuto-, touto- (people) [Oscan touto, Lithuanian tauta, Gothic thiuda, OI tu’ath]
trag- (a foot) [OI traig ‘a foot’]
tri (three) [IE *treyes, *tri ‘three’]
trougo- (unhappy)
uediiu (I pray; 1st sg. pres.)
ueramos (supreme, the highest)
uerno- (an alder)
uesu-, uisu- (king, cheerful) [IE *wesu- ‘good’]
uinom (wine; acc.sg. Lepontic) [Latin vinum, Greek oinos, Armenian ginu]
uiro- (a man, a husband) [IE *wiro- ‘a man’]
uros (a bull)
uxello- (high) [IE *upo-s- ‘above’, Greek hypsi ‘high’, OI uas ‘above’, Polish wysoki ‘high’]
vasso- (a servant)
ve’co- (fury, rage)
ver (above) [Russian verh ‘up, above’, Latvian virsus ‘up’, Sanskrit vars.ma ‘height’, Latin verruca ‘a rough’, OI ferr ‘better’]
vidu- (wood) [OI fid, Welsh guid, Cornish guiden, Old English wudu, Old High German witu]