I'm one mixed with TNT preparation (8)

I believe the answer is:

ointment

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'preparation' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'i'm one mixed with tnt' is the wordplay.
'mixed with' is an anagram indicator.
'im'+'one'='imone'
'imone' mixed up with 'tnt' gives 'OINTMENT'.

Can you help me to learn more?

(Other definitions for ointment that I've seen before include "Medication rubbed on skin" , "Lotion" , "Healing or cosmetic preparation" , "Salve or unguent" , "Medicated oily compound" .)

I've seen this clue in The Sun.

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