Minor complaint about horse entering river (6)
I believe the answer is:
niggle
'minor complaint' is the definition.
'niggle' can be an answer for 'complaint' (a minor complaint or quibble). I'm not certain of the 'minor' bit.
'horse entering river' is the wordplay.
'horse' becomes 'gg' (geegee or GG is a childish term for a horse).
'entering' is an insertion indicator.
'river' becomes 'nile' (Nile is an example).
'gg' going within 'nile' is 'NIGGLE'.
'about' is the link.
Can you help me to learn more?
(Other definitions for niggle that I've seen before include "Objection" , "Grumble" , "Trivial problem, fuss" , "Get" , "Carp" .)