Old boy in ship cries (4)
I believe the answer is:
sobs
'cries' is the definition.
(sobbing is a kind of crying)
'old boy in ship' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'in' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'ob' inserted into 'ss' is 'SOBS'.
(Other definitions for sobs that I've seen before include "showing distress" , "Weeps audibly" , "Weeps heavily (4)" , "Weeps heavily for boss" , "Weeps noisily" .)