Left a large gateway (6)
I believe the answer is:
portal
'gateway' is the definition.
(thesaurus)
'left a large' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'large' becomes 'l'.
'port'+'a'+'l'='PORTAL'
(Other definitions for portal that I've seen before include "Grand sort of entrance." , "An imposing door or gate" , "An imposing gateway" , "An imposing gate or doorway" , "Special website bringing together information from diverse sources in a uniform way" .)