Most of cheek in undergarments (4)
I believe the answer is:
bras
'undergarments' is the definition.
(bra is a kind of undergarment)
'most of cheek' is the wordplay.
'most of' means to remove the last letter.
'cheek' becomes 'brass' (brass neck can mean cheek or insolence).
'brass' with its last letter taken away is 'BRAS'.
'in' is the link.
(Other definitions for bras that I've seen before include "Items in womenswear" , "Female undergarments" , "They support" , "supports" , "intimate garments" .)