Accepted with hesitation, model was still (5)
I believe the answer is:
inert
'still' is the definition.
(not moving)
'accepted with hesitation model' is the wordplay.
'accepted' becomes 'in' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'model' becomes 'T' (Ford Model T car).
'in'+'er'+'t'='INERT'
'was' acts as a link.
(Other definitions for inert that I've seen before include "Unreactive; still" , "Not chemically reactive" , "Leaden" , "Unreacting" , "like nitrogen" .)