Timid type drops small grimace (4)
I believe the answer is:
moue
'grimace' is the definition.
(moue is a kind of grimace)
'timid type drops small' is the wordplay.
'timid type' becomes 'mouse' (I've seen this before).
'drops' suggests deleting specific letters.
'small' becomes 's' (abbreviation - e.g. clothes size).
'mouse' with 's' taken out is 'MOUE'.
(Other definitions for moue that I've seen before include "Disdainful pout" , "Face" , "expression of displeasure" , "Insolent pout" , "Expression of disdain" .)