Traveller wearing brown drill (6)
I believe the answer is:
trepan
'drill' is the definition.
(trepan is a kind of drill)
'traveller wearing brown' is the wordplay.
'traveller' becomes 'rep' (travel company worker).
'wearing' indicates putting letters inside.
'brown' becomes 'tan' (tan is a kind of brown).
'rep' inserted into 'tan' is 'TREPAN'.
(Other definitions for trepan that I've seen before include "Skull borer" , "Perforate skull (med.)" , "Surgically create a hole in the skull" , "old saw" , "Make perforation in person's skull" .)