Indication of highest tide that may be distinctly featured in the paper (9)
I believe the answer is:
watermark
'indication of highest tide that may be distinctly featured in the paper' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'indication of' is the wordplay.
I cannot quite see how this works, but
'indication' could be 'mark' (mark is a kind of indication) and 'mark' is located in the answer.
The remaining letters 'water' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for watermark that I've seen before include "Design in paper" , "faint pattern" , "Paper manufacturer's identification" , "Security device, on paper" , "Line showing maximum flood level" .)