Traveller departed without one carbon copy (9)
I believe the answer is:
replicate
'copy' is the definition.
(I know that copy can be written as replicate)
'traveller departed without one carbon' is the wordplay.
'traveller' becomes 'rep' (travel company worker).
'departed' becomes 'late' (late can mean deceased).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'one' becomes 'i' (Roman numeral).
'carbon' becomes 'C' (chemical symbol).
'i'+'c'='ic'
'late' enclosing 'ic' is 'licate'.
'rep'+'licate'='REPLICATE'
(Other definitions for replicate that I've seen before include "Make an exact copy of" , "Copy, reproduce" , "Copy exactly" .)