Exercise books on American tree rewritten as part of 18's work? (10)
I believe the answer is:
Here is my best explanation:
'part of 18's work?' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'exercise books on american tree rewritten' is the subsidiary indication.
'exercise' becomes 'pe'.
'books' becomes 'nt' (New Testament).
'on' means one lot of letters go next to another.
'american' becomes 'am' (abbreviation in some contexts).
'rewritten' indicates anagramming the letters.
'tree' with letters rearranged gives 'eter'.
'as' is the link.
(Other definitions for pentameter that I've seen before include "Verse line of 20 ac feet", "Typical Shakespearean line" and "Line of five metric feet".)