Immature flyer is rashly flying after cold (9)
I believe the answer is:
chrysalis
'immature flyer' is the definition.
(immature form of a butterfly or moth)
'is rashly flying after cold' is the wordplay.
'flying' indicates an anagram (letters fly around into new positions).
'after' means one lot of letters go next to another.
'cold' becomes 'c' (eg on taps).
'is'+'rashly'='israshly'
'israshly' anagrammed gives 'hrysalis'.
'hrysalis' after 'c' is 'CHRYSALIS'.
(Other definitions for chrysalis that I've seen before include "insect developing" , "Pre-butterfly stage" , "Dormant insect pupa" , "Cocooned pupa of a moth or butterfly" , "Pupa of an insect such as a butterfly" .)