Join a girl at ten (5)
I believe the answer is:
annex
'join' is the definition.
(I've seen this before)
'a girl at ten' is the wordplay.
'a girl' becomes 'anne' (girl's name).
'at' says to put letters next to each other.
'ten' becomes 'X' (Roman numeral).
'anne'+'x'='ANNEX'
(Other definitions for annex that I've seen before include "Attach after conquest" , "Appropriate" , "Addition to a document" , "Extension to a main building" , "Grab" .)