Individual catching cold in the past (4)
I believe the answer is:
once
'in the past' is the definition.
(I've seen this before)
'individual catching cold' is the wordplay.
'individual' becomes 'one' (**).
'catching' indicates putting letters inside.
'cold' becomes 'c' (eg on taps).
'one' enclosing 'c' is 'ONCE'.
(Other definitions for once that I've seen before include "Quick examination" , "At a previous time" , "not repeatedly" , "in days of yore?" , "In days gone by" .)