Six on round large instrument from long ago (4)
I believe the answer is:
viol
'instrument from long ago' is the definition.
I can't tell whether this definition defines the answer.
'six on round large' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'round' becomes 'o' (round can mean a round object).
'large' becomes 'L' (eg in clothes sizes).
'vi'+'o'+'l'='VIOL'
Can you help me to learn more?
(Other definitions for viol that I've seen before include "Old six-stringed instrument played with a bow" , "something from the past to play" , "Old stringed instrument" , "Precursor of the violin" , "Early bowed stringed instrument" .)