Stand-in starts to learn off Cambridge University master (5)
I believe the answer is:
Here is my best explanation:
'stand-in' is the definition.
(locum is a kind of stand-in)
'starts to learn off cambridge university master' is the subsidiary indication.
'starts to' suggests taking the first letters.
'cambridge university' becomes 'cu'.
'master' becomes 'm'.
The first letters of 'learn off' is 'lo'.
(Other definitions for locum that I've seen before include "Medical temp?", "A substitute or stand-in doctor", "Stand-in, for a doctor say", "Deputy doctor", "Professional temp", "Stand-in GP", "Temporary substitute", "Stand-in doctor, clergyman etc", "Stand-in medic" and "Professional who stands in for another".)