Stale (5)
(Other definitions for trite that I've seen before include "Banal, commonplace" , "Overfamiliar through overuse" , "Commonplace, hackneyed" , "used till novelty's worn off" , "repeated too often" .)
'stale' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for musty that I've seen before include "Stale and dank" , "Smelling stale or damp" , "Mouldy; stale-smelling" , "Frowsty" , "Stale, mouldy-smelling" .)