A friend on manuscript for POTUS, etc? (8)
I believe the answer is:
acronyms
'potus etc?' is the definition.
(POTUS is an acronym)
'a friend on manuscript' is the wordplay.
'friend' becomes 'crony' (crony is a kind of friend).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'manuscript' becomes 'ms' (abbreviation for manuscript).
'a'+'crony'+'ms'='ACRONYMS'
'for' acts as a link.
(Other definitions for acronyms that I've seen before include "entities formed initially, one can say" , "Words made from the initials of others" , "Words made from first letters of other words" , "Corny Sam makes words from first letters of other words" , "NICAM and the like" .)