Beaten hero with little energy — outwardly miserable grump (8)

'grump' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I can't see?

'beaten hero with little energy outwardly miserable' is the wordplay.
'beaten' indicates anagramming the letters (letters beaten up or destroyed).
'with' is a charade indicator (letters next to each other).
'little' indicates taking the first letters.
'outwardly' is an insertion indicator (some letters go outside others).
'miserable' becomes 'sad' (similar in meaning).
The initial letter of 'energy' is 'e'.
'hero' put after 'e' is 'ehero'.
'ehero' is an anagram of 'orehe'.
'orehe' placed inside 'sad' is 'SOREHEAD'.

Can you help me to learn more?