Slackened, past participle of slacken. Synonyms in the same form.
Abate
abated, slowed, relaxed, slacked, loosed, diminished, reduced, moderated, mitigated, lolled, retarded, dulled, bated, slaked
Loosen
loosened, eased, lessened, softened, allayed, mollified, alleviated, soothed, assuaged, palliated
Other
remitted
All synonyms for slacken →