Man absorbing girl's turn of phrase (5)
I believe the answer is:
idiom
'turn of phrase' is the definition.
(I've seen this before)
'man absorbing girl's' is the wordplay.
'man' becomes 'iom' (abbreviation for Isle of Man).
'absorbing' means one lot of letters goes inside another.
'girl' becomes 'Di'.
'iom' enclosing 'di' is 'IDIOM'.
(Other definitions for idiom that I've seen before include "characteristic use of language" , "Form of linguistic expression" , "Colloquialism" , "'Break a leg' or 'miss the boat'" , "Characteristic style of expression" .)