Word formed from the initial letters of others (7)
I believe the answer is:
acronym
'word formed from the initial letters of others' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for acronym that I've seen before include "Perhaps NATO" , "Ernie, for one" , "NATO's one" , "eg Ernie; radar" , "Mar cony (anag)" .)