Begin march among almost all Uni former students (6)
I believe the answer is:
alumni
'former students' is the definition.
(I've seen this before)
'begin march among almost all uni' is the wordplay.
'begin' indicates taking the first letters.
'among' is an insertion indicator (inserted letters are placed among others).
'almost' means to remove the last letter (most of the word but not all of it).
The first letter of 'march' is 'm'.
'all' with its last letter taken off is 'al'.
'al'+'uni'='aluni'
'm' inserted within 'aluni' is 'ALUMNI'.
(Other definitions for alumni that I've seen before include "Past pupils, former students" , "Past pupils of the old school" , "Former (college) students" , "Ex-students" , "Past pupils or graduates" .)