Gospeller to one side has small guitar (4)
I believe the answer is:
luke
'gospeller' is the definition.
(I've seen this before)
'one side has small guitar' is the wordplay.
'one side' becomes 'l'.
'has' means one lot of letters go next to another.
'small guitar' becomes 'uke' (uke is a kind of guitar. I am not sure about the 'small' bit.**).
'l'+'uke'='LUKE'
'to' is the link.
Can you help me to learn more?
(Other definitions for luke that I've seen before include "Gospel writer" , "Physician gospeller" , "One of the four Evangelists" , "Matthew, Mark, - - and John" , "Traditionally the author of the third Gospel" .)