"slack" en el diccionario Collins English Cobuild & Thesaurus

slack
adj

1 baggy, easy, flaccid, flexible, lax, limp, loose, not taut, relaxed

2 asleep on the job (informal) easy-going, idle, inactive, inattentive, lax, lazy, neglectful, negligent, permissive, remiss, slapdash, slipshod, tardy

3 dull, inactive, quiet, slow, slow-moving, sluggish
n

4 excess, give (informal) leeway, looseness, play, room
vb

5 bob off  (Brit. slang) dodge, flag, idle, neglect, relax, shirk, skive  (Brit. slang) slacken

Antonyms
,   adj

1 inflexible, rigid, stiff, strained, stretched, taut, tight

2 & 3 active, bustling, busy, concerned, diligent, exacting, fast-moving, hard, hard-working, hectic, meticulous, stern, strict