Tell raver to be composed, one on a trip (9)
I believe the answer is:
traveller
'one on a trip' is the definition.
(I've seen this before)
'tell raver to be composed' is the wordplay.
'to be composed' is an anagram indicator.
'tell'+'raver'='tellraver'
'tellraver' with letters rearranged gives 'TRAVELLER'.
(Other definitions for traveller that I've seen before include "He trips off" , "Itinerant" , "asked if anybody was there" , "Rep" , "'I met a . . . . . . . . . from an antique land' (P.B.Shelley)" .)