Agreement for one side on first of October (6)
I believe the answer is:
righto
'agreement for one' is the definition.
I can't tell whether this definition defines the answer.
'side on first of october' is the wordplay.
'side' becomes 'right' ().
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'first of october' becomes 'o' (rst letter of 'october').
'right'+'o'='RIGHTO'
Can you help me to learn more?
(Other definitions for righto that I've seen before include "Okay!" , "very well" , "Correct" , "Informal expression of agreement or acceptance" , "Agreed" .)