Authorise measure by earl for one (7)
I believe the answer is:
entitle
'authorise' is the definition.
(entitling is a kind of authorizing)
'measure by earl for one' is the wordplay.
'measure' becomes 'en' (typographical measure).
'by' says to put letters next to each other.
'earl for one' becomes 'title' (I can't explain this - if you can you should give a lot more credence to this answer).
'en'+'title'='ENTITLE'
Can you help me to learn more?
(Other definitions for entitle that I've seen before include "Qualify, empower" , "Licence" , "Give a right or authority to" , "Give (someone) rights" , "Allow" .)