Little robot cat? Not so unfathomable! (10)

I believe the answer is:

bottomless

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'unfathomable' is the definition.
(similar in meaning)

'little robot cat? not' is the wordplay.
'little robot cat?' becomes 'bottom' (I can't explain this - if you can you should give a lot more credence to this answer).
'not' becomes 'less' (I've seen this in other clues).
'bottom'+'less'='BOTTOMLESS'

'so' is the link.

Can you help me to learn more?

(Other definitions for bottomless that I've seen before include "Very deep" , "Inexhaustible" , "Unfathomable" , "Having no limits" , "Quince thus was in a jam" .)

I've seen this clue in the Sydney Morning Herald.

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