Stick flexible as putty (4,3)
I believe the answer is:
stay put
'stick' is the definition.
(synonyms)
'flexible as putty' is the wordplay.
'flexible' indicates anagramming the letters (I've seen this in other clues).
'as'+'putty'='asputty'
'asputty' with letters rearranged gives 'STAY PUT'.
(Other definitions for stay put that I've seen before include "Remain unmoving" , "Remain in one place" , "Stick around" , "Informally, don't move - remain in situ" , "Remain in place, don't move" .)