Crossword Genius

Mostly stupid dirty dog or little piggy? (5)

Ross

I believe the answer is:

digit

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

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

'mostly stupid dirty dog' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'stupid' becomes 'dim' (similar in meaning).
'dirty dog' becomes 'git' (I can't explain this - if you can you should believe this answer much more).
'dim' with its last letter removed is 'di'.
'di'+'git'='DIGIT'

'or' acts as a link.

Can you help me to learn more?

(Other definitions for digit that I've seen before include "One in ten, say" , "Finger; number" , "A character" , "One's on hand" , "Single numeral" .)

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