Bit of small kiss (5)
I believe the answer is:
speck
'bit' is the definition.
(I have seen 'Bit of dust ' mean 'speck' so perhaps 'bit' could also mean 'speck')
'small kiss' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'kiss' becomes 'peck' (pecking is a kind of kissing).
's'+'peck'='SPECK'
'of' is the link.
(Other definitions for speck that I've seen before include "Small mark" , "Bit of dust" , "Italian ham" , "Dot" , "Small spot" .)