Conjecture, theorise (9)
I believe the answer is:
speculate
This clue is a double definition.
'conjecture' is the first definition.
(I know that conjecture can be written as speculate)
'theorise' is the second definition.
(I know that theorise can be written as speculate)
(Other definitions for speculate that I've seen before include "Guess without knowing the facts" , "Play the market" , "Imagine" , "Bet; theorise" , "Buy in hope of profit, but with risk of loss" .)