Jocular desire to rein in a child's horse (7)
I believe the answer is:
waggish
'jocular' is the definition.
(thesaurus)
'desire to rein in a child's horse' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'horse' could be 'gg' (geegee or GG is a childish term for a horse) and 'gg' is found in the answer.
'desire' could be 'wish' (wish is a kind of desire) and 'wish' is found in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for waggish that I've seen before include "Facetious" , "Said in a joking way, like dog's tail in motion?" , "Playfully humorous" .)