See about trainer regularly entering college (5)
I believe the answer is:
oriel
'college' is the definition.
(Oxford University college)
'see about trainer regularly entering' is the wordplay.
'see' becomes 'lo' (archaic exclamation meaning 'look!').
'about' says the letters should be written backwards.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'entering' indicates putting letters inside.
The alternating letters of 'trainer' are 'rie'.
'lo' in reverse letter order is 'ol'.
'ol' placed around 'rie' is 'ORIEL'.
(Other definitions for oriel that I've seen before include "Upstairs bay window" , "Type of bay window" , "lecturer seen near Lorraine regularly" , "Style of window" , "First-floor bay (window)" .)