Cadence (6)
'cadence' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rhythm that I've seen before include "(Musical) stress pattern" , "Musical beat or pattern" , "Pattern of recurrence (of sound)" , "Recurring pattern" , "Pattern of movement or sound" .)
(Other definitions for tone that I've seen before include "Quality of a person's voice" , "Sound signal on a telephone" , "Bodily firmness" , "Quality of sound, voice say" , "Theobald Wolf . . . ." .)