Way to describe popular comedian's act (7)
I believe the answer is:
routine
'comedian's act' is the definition.
(I've seen this before)
'way to describe popular' is the wordplay.
'way' becomes 'route' (route is a kind of way).
'to describe' indicates putting letters inside.
'popular' becomes 'in' ('in' can mean trendy).
'route' going around 'in' is 'ROUTINE'.
(Other definitions for routine that I've seen before include "Usual pattern of actions" , "Ordinary" , "The daily round" , "Everyday procedure" , "Fixed programme" .)