Uncertain factors (3)
I believe the answer is:
ifs
'uncertain factors' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ifs that I've seen before include "No ...,ands or buts, no argument allowed" , "Suppositions, may be accompanied by buts" , "If . . . and ands were pots and pans" , "Conditional conjunctions" , "Conditions or suppositions, may join with buts" .)