Constrained style of book, long dull volume with Gaelic appendix (5,5)

'gaelic appendix' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I don't see?

'constrained style of book long dull volume' is the wordplay.
I cannot really understand how this works, but
'style' could be 'verse' (verse is a kind of style) and 'verse' is found in the answer.
'book' could be 'b' (abbreviation for book) and 'b' is located in the answer.
'long' could be 'lank' (I've seen this before) and 'lank' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

'with' acts as a link.

Can you help me to learn more?