Monotreme's dicky ticker (9)
I believe the answer is:
metronome
'ticker' is the definition.
(I've seen this before)
'monotreme's dicky' is the wordplay.
'dicky' indicates an anagram (dicky can mean ill or non-functioning).
'monotreme' anagrammed gives 'METRONOME'.
(Other definitions for metronome that I've seen before include "Ticker setting tempo of music" , "Musician's timekeeper" , "Device to help regulate tempo" , "Instrument for beating time in music" , "Musical timekeeper" .)