Hesitation at the summit he drinks too much! (5)
I believe the answer is:
toper
'he drinks too much' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'hesitation at the summit' is the wordplay.
'hesitation' becomes 'er' (sound used when hesitating).
'at' says to put letters next to each other (I've seen this in other clues).
'the summit' becomes 'top' ('top' can be a synonym of 'summit').
'er' put after 'top' is 'TOPER'.
Can you help me to learn more?
(Other definitions for toper that I've seen before include "Serious drinker" , "Tippler" , "boozer" , "Trope for habitual drinker" , "Alcoholic" .)