Slacken – slow / brake / diminish / loosen/ abate / retard / detain
Antonym – tighten /enlarge / accelerate / intensify
It is a verb .
Rampage –
As noun –
storm / rage / violence / binge / disturbance / frenzy
Antonym – calm / happiness / quiet / tranquillity
As verb –
fulminate / bluster / rave / carry on
Antonym – restrain / check
Annihilation – extinction / abolishment / annulment / destruction / extermination / devastation / eradication / decimation / elimination
Antonym – construction / rescue / building / beginning
It is a noun.
Trample – crush / stomp / smash / infringe / override / encroach
Antonym – assist / uncompress
It is a verb.
Stray – homeless / scattered / erratic / arbitrary / vagrant / roaming / meander / wander / drift
Antonym – remain / systematic / regular / stay
It is an adjective.
Fanatic – extremist / addict / enthusiast / bigot / lover / maniac / devotee / sucker
Antonym – conservative / moderate / detractor / critic
It is a noun.
Fabulous – fantastic / outrageous /incredible / legendary / astonishing / mythic / marvellous / awesome
Antonym – inferior / ordinary / real / normal / unremarkable
It is an adjective.