One agreement about another for couples (5)
I believe the answer is:
yokes
'for couples' is the definition.
('yoke' can be a synonym of 'couple')
'one agreement about another' is the wordplay.
'one agreement' becomes 'ok' (I've seen this in other clues).
'about' is an insertion indicator.
'another' becomes 'yes' (I can't justify this - if you can you should believe this answer much more).
'ok' put inside 'yes' is 'YOKES'.
Can you help me to learn more?
(Other definitions for yokes that I've seen before include "Crosspieces fastened over the necks of a pair of draft animals" , "couples" , "Harnesses (oxen)" , "Oppresses" , "Harnesses together" .)