Stay flexible also in motion (8)
I believe the answer is:
proposal
'motion' is the definition.
(I've seen this before)
'stay flexible also in' is the wordplay.
'stay' becomes 'prop' (I've seen this before).
'flexible' indicates an anagram (I've seen this in other clues).
'in' is an insertion indicator.
'also' with letters rearranged gives 'osal'.
'prop' placed within 'osal' is 'PROPOSAL'.
(Other definitions for proposal that I've seen before include "Offer (to get spliced?)" , "put before the union?" , "Offer - suggestion" , "union offer?" , "a match might be arranged?" .)