A surname? Everybody has one (5)
I believe the answer is:
allan
'a surname?' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
'everybody has one' is the wordplay.
'everybody' becomes 'all' (I've seen this before).
'has' says to put letters next to each other.
'one' becomes 'an' (I've seen this in other clues).
'all'+'an'='ALLAN'
Can you help me to learn more?
(Other definitions for allan that I've seen before include "Man" , "Man's name" , "-- Quartermain (Rider Haggard)" , "Edgar ____ Poe, poet and short story writer (1809-49)" .)