Behold one’s girl (4)
I believe the answer is:
lois
'girl' is the definition.
'behold one's' is the wordplay.
'behold' becomes 'lo' (archaic exclamation meaning 'look!').
'one's' becomes 'is' (Roman numeral).
'lo'+'is'='LOIS'
(Other definitions for lois that I've seen before include "Woman" , "- Lane, Daily Planet reporter" , "- Lane (Superman's girl)" , "-- Lane, 'Superman' character" , "- Lane, girlfriend of Superman" .)