Conceivable, imaginable (8)
I believe the answer is:
possible
I believe this is a double definition.
'conceivable' is the first definition.
(similar in meaning)
'imaginable' is the second definition.
(thesaurus)
(Other definitions for possible that I've seen before include "Capable of being achieved" , "Achievable, able to be done" , "Feasible achievable" , "Capable of happening" , "Conceivable, practicable" .)