RALLENTANDO

rallentando, ritardando, ritenuto, rit.

(adjective) (music) gradually decreasing in tempo

rallentando

(adverb) slowing down; “this passage should be played rallentando”

Source: WordNet® 3.1

Etymology

Adjective

rallentando (not comparable)

(music) slackening; becoming slower (used as a musical direction).

Source: Wiktionary

Ral"len*tan"do, a. Etym: [It.] (Mus.)

Definition: Slackening; -- a direction to perform a passage with a gradual decrease in time and force; ritardando.

Source: Webster’s Unabridged Dictionary 1913 Edition