Behold new professor from the Big Smoke (6)
I believe the answer is:
london
'the big smoke' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'behold new professor' is the wordplay.
'behold' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'professor' becomes 'don' (term for a university professor).
'lo'+'n'+'don'='LONDON'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for london that I've seen before include "US writer" , "England's capital city" , "Construction across the Thames near the Monument" , "Jack - , US author (White Fang); city" , "UK's capital" .)