Small, vain creep? (5)
I believe the answer is:
sidle
'creep?' is the definition.
(both can mean to move secretly or quietly)
'small vain' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'vain' becomes 'idle' (I've seen this in another clue).
's'+'idle'='SIDLE'
(Other definitions for sidle that I've seen before include "Make cautious progress" , "Slide (anag.)" , "Edge along furtively" , "Walk obliquely" , "Move in furtive manner, edge along" .)