Moving north - that is sharp (5)
I believe the answer is:
thorn
'sharp' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'moving north' is the wordplay.
'moving' indicates anagramming the letters (letters are moved around).
'north' with letters rearranged gives 'THORN'.
'that is' is the link.
Can you help me to learn more?
(Other definitions for thorn that I've seen before include "Letter written long ago" , "Spine - prickle - Old English runic letter" , "Pointed extension of leaf" , "Plant spine; old letter" , "irritation when in one's side" .)