Trod water, perhaps, with one teacher (5)
I believe the answer is:
swami
'teacher' is the definition.
(Hindu religious teacher)
'trod water perhaps with one' is the wordplay.
'trod water perhaps' becomes 'swam' (treading water is a type of swimming).
'with' means one lot of letters go next to another.
'one' becomes 'I' (Roman numeral).
'swam'+'i'='SWAMI'
(Other definitions for swami that I've seen before include "Indian religious teacher" , "Hindu leader" , "Teacher abroad" , "Hindu mystic" , "Guru" .)