Edinburgh University now upsets principals. Companion follows harem guard (6)
I believe the answer is:
eunuch
'harem guard' is the definition.
(I've seen this before)
'edinburgh university now upsets principals companion follows' is the wordplay.
'principals' indicates taking the first letters.
'companion' becomes 'ch' (Companion of Honour).
'follows' is a charade indicator (letters next to each other).
The initial letters of 'edinburgh university now upsets' is 'eunu'.
'eunu'+'ch'='EUNUCH'
(Other definitions for eunuch that I've seen before include "Ineffectual man" , "Feeble person" , "Powerless type" , "Keeper of a harem" , "Emasculated man" .)