Tenor keeping money for annuity scheme (7)
I believe the answer is:
tontine
'annuity scheme' is the definition.
(type of investment scheme)
'tenor keeping money' is the wordplay.
'tenor' becomes 'tone' (synonyms).
'keeping' means one lot of letters goes inside another.
'money' becomes 'tin' (old-fashioned slang term for money).
'tone' placed around 'tin' is 'TONTINE'.
'for' is the link.
(Other definitions for tontine that I've seen before include "financial enterprise" , "financial scheme" , "Tin tone for a scheme of life annuity" , "life assurance scheme" .)