Truism (9)
I believe the answer is:
platitude
'truism' is the definition.
(platitude is a kind of truism)
This is all the clue.
(Other definitions for platitude that I've seen before include "Familiar tune" , "Commonplace remark uttered as if original" , "Common place, say" , "Trite remark made as if meaningful" , "Empty remark" .)