Flexible and carefree? Not at first (5)
I believe the answer is:
lithe
'flexible' is the definition.
(thesaurus)
'carefree? not at first' is the wordplay.
'carefree?' becomes 'blithe' ('blithe' can be a synonym of 'carefree').
'not at first' means to remove the first letter.
'blithe' with its first letter removed is 'LITHE'.
'and' acts as a link.
(Other definitions for lithe that I've seen before include "Don -, opera by Verdi" , "Svelte" , "Lissom, supple" , "Slender, supple" , "Supple and graceful" .)