Reason one invested in record clubs (5)
I believe the answer is:
logic
'reason' is the definition.
(I've seen this in another clue)
'one invested in record clubs' is the wordplay.
'one' becomes 'i' (Roman numeral).
'invested in' means one lot of letters goes inside another.
'record' becomes 'log' (log is a kind of record).
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'log'+'c'='logc'
'i' placed inside 'logc' is 'LOGIC'.
(Other definitions for logic that I've seen before include "4-ing" , "System of reasoning" , "The science of reasoning correctly" , "subject with 14 [ARGUMENTS]" , "this makes sense" .)