The term 'CERTAIN TO HAPPEN' can be described by four crossword solutions: EVENTUAL (8 letters), ASSURED (7 letters), FATED (5 letters), and INEVITABLE (10 letters). EVENTUAL means that something will happen eventually, but not necessarily soon. ASSURED implies that something is certain to happen, and is often used to describe a guarantee or promise. FATED suggests that something is predetermined and unavoidable. Finally, INEVITABLE implies that something is certain to happen and cannot be avoided.