The minute gear changes accompanying variable cycling speed (9)
I believe the answer is:
megahertz
'cycling speed' is the definition.
The answer and definition can be both related to time as well as being singular nouns.
Maybe there's a link between them I don't understand?
'the minute gear changes accompanying variable' is the wordplay.
'minute' becomes 'm' (abbreviation).
'changes' is an anagram indicator.
'accompanying' means one lot of letters go next to another.
'variable' becomes 'z' (algebra).
'the'+'m'+'gear'='themgear'
'themgear' is an anagram of 'megahert'.
'megahert'+'z'='MEGAHERTZ'
Can you help me to learn more?
(Another definition for megahertz that I've seen is " MHz in full".)