Almost cover horse, competent? Too difficult (14)
I believe the answer is:
insurmountable
'difficult' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'almost cover horse competent? too' is the wordplay.
I cannot quite see how this works, but
'horse' could be 'mount' (mount is a kind of horse) and 'mount' is present in the answer.
'competent?' could be 'able' (similar in meaning) and 'able' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for insurmountable that I've seen is " Too great to be overcome".)