Horrid and nasty, terribly up itself (8)

I believe the answer is:

spiteful

I'm a little stuck... Click here to teach me more about this clue!

'horrid and nasty' is the definition.
I can't tell whether this definition defines the answer.

'terribly up itself' is the wordplay.
'terribly' is an anagram indicator.
'up'+'itself'='upitself'
'upitself' anagrammed gives 'SPITEFUL'.

Can you help me to learn more?

(Other definitions for spiteful that I've seen before include "Malevolent, wanting to hurt" , "Vengeful, malicious" , "With desire to hurt" , "Showing malice" , "nasty!" .)

I've seen this clue in The Telegraph.

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