Understood 1ac anagram in Times (5)
I believe the answer is:
tacit
'understood' is the definition.
(I've seen this before)
'1ac anagram in times' is the wordplay.
'iac' becomes 'ac'.
'anagram' becomes 'i' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'times' becomes 'tt' (two abbreviations for time).
'ac'+'i'='aci'
'aci' inserted within 'tt' is 'TACIT'.
(Other definitions for tacit that I've seen before include "Implicitly understood" , "Implied without being said" , "Aircraft engine casing" , "Understood, not spoken or played" , "Attic? (anag)" .)