Synonyms are words or phrases of the same grammatical class that have a similar meaning as another in the same language. Slay and kill are synonyms.

A list of synonyms is given below:
abbreviate abridge, condense
abandon leave, forsake, forgo
abate decrease, lessen, diminish
ability capability, competence
abrupt sudden, nasty
abnormal unusual, eccentric, irregular
aboriginal primitive, primeval
abridge shorten, condense, compress
abundance plenty, profusion, fullness
abstain refrain, forbear
absurd ridiculous
accomplish achieve
accumulate collect, store
acute keen, sharp
adequate sufficient, enough
admiration praise, esteem
adoration worship, reverence
alien foreign
amicable friendly
anger ire, wrath, rage
apt appropriate, suitable
ascend rise, soar, climb
assistance aid, help
astonish amaze, surprise,
audacious bold, daring
authentic genuine
autocrat despot
avaricious greedy
aversion dislike, hostility, hatred
awkward clumsy
banish exile, dismiss, expel
blame accuse
bliss joy, happiness
bogus false, counterfeit, spurious
bondage slavery
brave courageous, bold
brief concise, short
brilliant sparkling, bright, intelligent
brisk vigorous
bystander spectator, onlooker
calm quiet, tranquil
candid frank,
casual occasional
colossal huge, gigantic
command order
compel coerce, force
comprehend understand
concise short, brief, passionless
condense compress
confess admit
confuse confound, perplex
cordial warm, hearty, friendly
conscious aware
crucial critical, decisive, severe
contrary opposite
conversant familiar
cheat deceive, fraud
destitute needy
despise scorn, disdain
didactic instructive
dismal gloomy
divine godly, heavenly
dexterity skill, deftness, cleverness
disgrace dishonour, shame
diligent industrious
divide part, separate
detest hate, dislike, despite, loathe, abhor
dear valuable, costly, cherished
dim vague
durable enduring, lasting
eager earnest, ardent
earnest eager, serious
eccentric odd, peculiar
economical frugal
efficient able, competent
elegant tasteful, refined, graceful
emancipation freedom, liberty, deliverance
emphasize stress
emulate imitate
enormous huge, immense
extravagant wasteful, prodigal
exquisite excellent, fine
exceptional rare, unusual
eminence importance, distinction
essential necessary, indispensable
examine  inspect, scrutinize, review 
famous celebrated, renowned
fanciful imaginative, visionary
fantastic strange, odd,
fascinate charm, enchant, bewitch, captivate
feeble weak, infirm
ferocious savage, fierce, barbarous
fictitious false, imaginary
fit suitable, proper, appropriate
foolish silly, stupid
fraud deceit, trickery, cheat
flimsy silly, slight, trivial
frank open, candid
fury  anger, rage, frenzy
general universal
gentle tender, mild, kind
genuine real, unaffected, sincere
gigantic huge, colossal
greedy avaricious, rapacious
grief sorrow, affliction
guard defend, protect
guilt crime, sin
guile fraud, trickery
habit custom, practice
habitual usual, customary, routine
hasty quick, swift., rapid, speedy
haughty arrogant, proud
hamper hinder, impede, block
hazardous risky, perilous
holy sacred
humane kind
humble meek
humility politeness, meekness, modesty
idle lazy
illegal unlawful, lawless
illiterate uneducated
immaterial unimportant, insignificant
imminent impending
increase augment, enlarge
initiate vex, annoy
indignant angry
inanimate lifeless
ingenuous artless, sincere
intimate close, inform
impostor cheat
inexorable relentless
insidious treacherous; crafty
Jealous envious
 jolly jovial, merry
jubilant joyful
judicious wise, prudent, discreet
just fair, impartial
juvenile youthful
keen sharp
keeper custodian
kind benevolent
lament mourn
latent dormant, hidden
liberty freedom, independence
liberal generous
lenient mild
laborious industrious, diligent
lethargy laziness, idleness, sluggishness
loathe hate, detest, abhor
likeness similarity, resemblance
lively active
loyal faithful, devoted
luxuriant abundant, profuse 
meagre small
malady disease, illness
mean low, abject
misery sorrow, sad
mournful sorrowful, sad
morbid unhealthy
mockery ridicule
malice spite, ill-will
magnificent splendid, grand 
notable remarkable
notorious infamous
nervous fearful, timid
norm standard
novelty newness
novice  beginner
obscene filthy, indecent, vulgar
obsolete antiquate
odd strange, peculiar
opportune timely
opportunity  chance
Pious devout, godly, religious
portray delineate, depict, sketch
prattle chatter, babble
prodigal extravagant, wasteful
profuse lavish
pathetic moving, touching
precarious  dangerous, risky 
queer strange, odd
quest  search, pursuit
radiant bright, brilliant
refined elegant, polished
rebellion revolt, mutiny
reiterate repeat
rare scarce
respect regard, esteem
renown frame, reputation
remorse repentance
rejoice exult, delight
relevant pertinent
resistance opposition
ruin destruction, downfall
rigid unyielding, stiff
remote distant, far
ridiculous absurd, laughable
sane wise, sensible, sound
sacred holy, consecrated
savage wild, uncivilized, barbarous
sly crafty, cunning
sympathy compassion
solitary single, lonely
shrewd astute, perspicacious
snug neat, trim, clean
servile slavish
shy bashful, coy
simple plain, natural
solace relief, comfort
slender slight, scanty
sordid dirty, ugly, squalid
specimen model, sample
splendid grand, magnificent
static fixed
spurious false, imaginary
sterile barren, unproductive
stationary fixed, motionless
sublime exalted, elevated
superficial shallow
synonyms identical, similar, equivalents 
tame gentle, mild, insipid
temporal worldly, materialistic
temperate moderate
tentative experimental
transient temporary, transitory
tradition convention, custom
teach educate, instruct
tyrant autocrat, despot 
ultimate final, last
unique incomparable, unequalled
urbane courteous, polite
urge incite, press
useful advantageous, beneficial
unduly  excessively
vacant empty
venerable respectable
vindictive revengeful
vehemence force, emphasis
vigilance watchfulness
vanquish defeat, conquer
vulgar indecent 
weary tired
wealthy rich
wild savage
wreck destroy, ruin
winsome charming, attractive
withstand resist
wavering unsteady, faltering
yield surrender
yearn crave, desire 
zeal fervour, eagerness, passion
zenith summit, top, pinnacle
zest  enthusiasm, gusto