Single traveller's nose (5)
I believe the answer is:
aroma
'nose' is the definition.
(I've seen this before)
'single traveller's' is the wordplay.
'single' becomes 'a'.
'traveller' becomes 'roma' (as in Romani Travellers).
'a'+'roma'='AROMA'
(Other definitions for aroma that I've seen before include "Subtle quality" , "Fragrance of spices" , "Pervasive quality" , "Pervasive atmosphere" , "Distinctive smell" .)