Cooker is new being in fashion (5)
I believe the answer is:
range
'cooker' is the definition.
(thesaurus)
'new being in fashion' is the wordplay.
'new' becomes 'n'.
'being in' means one lot of letters goes inside another.
'fashion' becomes 'rage' (rage is a kind of fashion**).
'n' placed inside 'rage' is 'RANGE'.
'is' acts as a link.
(Other definitions for range that I've seen before include "Set < compass" , "Cooking appliance" , "Compass - scope" , "Large, grassy land for livestock in the US" , "cover a certain area" .)