Model in non-U outfit (3)
I believe the answer is:
sit
'model' is the definition.
(e.g. for a painting)
'non-u outfit' is the wordplay.
'non' indicates named letters should be taken away.
'outfit' becomes 'suit' (suit is a type of outfit).
'suit' with 'u' removed is 'SIT'.
'in' is the link.
(Other definitions for sit that I've seen before include "Pose (for artist)" , "Take (an examination)" , "To take the test" , "Take a chair" , "Perch" .)