Outline, for the many on the trip (7)
I believe the answer is:
contour
'outline' is the definition.
(contouring is a kind of outlining)
'the many on the trip' is the wordplay.
'the many' becomes 'c' (C is the Roman numeral for 100).
'the trip' becomes 'tour' (I've seen this before).
'c'+'on'+'tour'='CONTOUR'
'for' is the link.
(Other definitions for contour that I've seen before include "Line on map indicating height" , "Map line of equal altitude" , "Silhouette" , "Outline (of land)" , "Outline, shape" .)