"clack" in the noun sense
1. clack, clap
a sharp abrupt noise as if two objects hit together may be repeated
2. clack valve, clack, clapper valve
a simple valve with a hinge on one side allows fluid to flow in only one direction
"clack" in the verb sense
1. clatter, clack, brattle
make a rattling sound
2. cluck, click, clack
make a clucking sounds, characteristic of hens
3. chatter, piffle, palaver, prate, tittle-tattle, twaddle, clack, maunder, prattle, blab, gibber, tattle, blabber, gabble
speak (about unimportant matters) rapidly and incessantly
Source: WordNet® (An amazing lexical database of English)
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