He'd dare to upset one reputed to be quick-tempered (7)
I believe the answer is:
redhead
'he'd dare to upset one reputed to be quick-tempered' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he'd dare to upset' is the wordplay.
'to upset' is an anagram indicator.
'hed'+'dare'='heddare'
'heddare' anagrammed gives 'REDHEAD'.
Can you help me to learn more?
(Other definitions for redhead that I've seen before include "Ginger-haired person" , "diving duck?" , "One with auburn hair" , "Auburn type" , "One with rufous hair" .)