Past and present, for two (6)
I believe the answer is:
tenses
'past and present for two' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tenses that I've seen before include "Tightens up" , "Becomes stretched or taut" , "Tautens; verb forms" , "'Past and present, say (6)'" , "Verb forms indicating time" .)