Shy boy meets retiring girl (5)
I believe the answer is:
timid
'shy' is the definition.
(synonyms)
'boy meets retiring girl' is the wordplay.
'boy' becomes 'tim' (short for Timothy).
'meets' is a charade indicator (letters next to each other).
'retiring' is a reversal indicator.
'girl' becomes 'Di' (short for Diane or Diana).
'di' backwards is 'id'.
'tim'+'id'='TIMID'
(Other definitions for timid that I've seen before include "Shrinking" , "Not assertive, retiring" , "Easily frightened" , "Lacking in courage" , "Inclined to avoid people" .)