Formerly suspended, one's dismissed (4)
I believe the answer is:
once
'formerly' is the definition.
(I know that formerly can be written as once)
'suspended one's dismissed' is the wordplay.
'suspended' becomes 'on ice' (to put something 'on ice' is to postpone it).
'one' becomes 'i' (Roman numeral).
'dismissed' indicates named letters should be taken away.
'onice' with 'i' taken out is 'ONCE'.
(Other definitions for once that I've seen before include "in days of yore?" , "On a single (or past) occasion" , "On one occasion" , "At some time past" , "Quick examination" .)