Idea about army musicians’ method of writing (8)
I believe the answer is:
notation
'writing' is the definition.
(I've seen this before)
'idea about army' is the wordplay.
'idea' becomes 'notion' (notion is a kind of idea).
'about' means one lot of letters goes inside another.
'army' becomes 'ta' (abbreviation for Territorial Army).
'notion' going around 'ta' is 'NOTATION'.
'musicians' method of' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for notation that I've seen before include "At noon it becomes a written note" , "System of musical symbols" , "Symbolic writing system" , "Set of representative symbols" , "System of signs or symbols" .)