Hot outside, one keeps under cover (5)
I believe the answer is:
hides
'keeps under cover' is the definition.
Although both the answer and definition are verbs in their -s form, I can't see how they can define each other.
'hot outside one' is the wordplay.
'hot' becomes 'h' (abbreviation eg on taps).
'outside' says to put letters next to each other (outside can mean adjacent to).
'one' becomes 'ides' (I am not sure about this - if you are sure you should believe this answer much more).
'h'+'ides'='HIDES'
Can you help me to learn more?
(Other definitions for hides that I've seen before include "screens" , "lies low" , "coats" , "Cloaks" , "Conceals or takes cover" .)