Traveller's time elsewhere interrupted by teacher coming over (7)
I believe the answer is:
tourist
'traveller's' is the definition.
(tourist is a kind of traveller)
'time elsewhere interrupted by teacher coming over' is the wordplay.
'time' becomes 't' (abbreviation).
'elsewhere' becomes 'out' (I've seen this in other clues).
'interrupted by' indicates putting letters inside.
'teacher' becomes 'sir' (way of addressing a male teacher).
'coming over' says the letters should be written in reverse.
'sir' written backwards gives 'ris'.
'out' enclosing 'ris' is 'ourist'.
't'+'ourist'='TOURIST'
(Other definitions for tourist that I've seen before include "Cheap travel class" , "Tripper, sightseer" , "Holiday visitor" , "Someone who travels for pleasure" , "Visiting sightseer" .)