Sentimental infiltrator given work (5)
I believe the answer is:
soppy
'sentimental' is the definition.
(I know that sentimental can be written as soppy)
'infiltrator given work' is the wordplay.
'infiltrator' becomes 'spy' (I've seen this in another clue).
'given' indicates putting letters inside.
'work' becomes 'op' (abbreviation for opus).
'spy' enclosing 'op' is 'SOPPY'.
(Other definitions for soppy that I've seen before include "Informally sentimental in sickly way" , "Indulgently sentimental" , "Feeble; sentimental" , "Overly sentimental" , "Thoroughly wet" .)