Second function for a very shy type (5)
I believe the answer is:
mouse
'a very shy type' is the definition.
'second function' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'function' becomes 'use' ('use' can be a synonym of 'function').
'mo'+'use'='MOUSE'
'for' is the link.
(Other definitions for mouse that I've seen before include "Small rodent and cursor controller" , "Rodent (for computing)" , "Small rodent - computer device" , "computer operator" , "See 1 down" .)