Crossword Genius

It's a singular cereal! (3)

Ross

I believe the answer is:

oat

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

'singular cereal' is the definition.
(I've seen this before)

'it's a' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
A single letter 'o' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for oat that I've seen before include "Cereal grass" , "Cereal (singular)" , "Basis of porridge" , "Cereal plant" , "Food grain" .)

I've seen this clue in the Evening Standard.
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