Initially an organisation (3)
I believe the answer is:
uno
'initially an' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'organisation' is the wordplay.
I cannot quite see how this works, but
'organisation' could be 'un' (the United Nations is an organisation) and 'un' is present in the answer.
A single letter 'o' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for uno that I've seen before include "One in Italy" , "card game" .)