Note that it's a fencing position (6)
I believe the answer is:
octave
'note' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for octave that I've seen before include "Series of eight consecutive musical notes" , "A verse of eight lines" , "Musical interval doubling note frequency" , "Set of eight musical notes" , "A fence standing" .)