Completely hot, will melt, more or less (10)
I believe the answer is:
thoroughly
'completely' is the definition.
(I've seen this before)
'hot will melt more or less' is the wordplay.
I cannot quite see how this works, but
an anagram of 'hot' is 'tho' which is located in the answer.
'more or less' could be 'roughly' (synonyms) and 'roughly' is found within the answer.
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 thoroughly that I've seen before include "Musical with Julie Andrews" , "More than a bit" , "Completely" , "Quite" , "Really" .)