I. ˌrēˌtärˈdän(ˌ)dō, -dan- adverb (or adjective)
Etymology: Italian, from Latin retardandum, gerund of retardare to retard — more at retard
: with a gradual slackening in tempo : rallentando — used as a direction in music
II. noun
( -s )
1. : a movement or passage in gradually slackening tempo
2. : a gradually slackening tempo