Volume with Gaelic language poetry (5)
I believe the answer is:
verse
'poetry' is the definition.
(synonyms)
'volume with gaelic language' is the wordplay.
'volume' becomes 'v' (abbreviation for volume in book titles).
'with' means one lot of letters go next to another.
'gaelic language' becomes 'erse' (term for the Scottish or Irish language).
'v'+'erse'='VERSE'
(Other definitions for verse that I've seen before include "Section of a poem" , "Poetry - subdivision of the Bible" , "Part of a song or poem" , "Literature in metrical form" , "Metrical text" .)