Some icon of fashion not constant (2-3)
I believe the answer is:
on-off
'not constant' is the definition.
(on-off can mean irregular or sporadic)
'some icon of fashion' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ON-OFF' can be found hidden inside 'icon of fashion'.
(Other definitions for on-off that I've seen before include "in bursts" , "Discontinuous" .)