What is, or was the meaning of "oncommon"?

In Dickens' David Copperfield, there is an exchange between David and Mr Pegotty who arrives with his nephew Ham to visit him at school. It runs as follows:

"Do you know how mama is, Mr Peggotty? I said. And how my dear, dear old Peggotty is?

'Oncommon' said Mr Peggotty.

'And little Em'ly, and Mrs Gummidge?'

'On--common', said Mr Peggotty.

And following a further exchange Peggotty continues:

…I was to come over and inquire for Mas'r Davy and give her dooty, humbly wishing him well and reporting of the fam'ly as they was oncommon toe-be-sure. Little Em'ly, you see, she'll write to my sister when I go back, as I see you and as you was similarly oncommon, and so we make it quite a merry-go-rounder.

Clearly oncommon means something like "in the best of health" but not only is it not quoted in the OED - even as an historic archaism - but as one who grew up close to the Norfolk dialect, which Peggotty speaks, it is unfamiliar to me too.

Dickens frequently wrote his characters' dialog in eye dialect, and his characters also frequently speak with non-standard grammar, often with characteristic quirks or catchphrases.

So I'd interpret oncommon as an eye-dialect representation of uncommon, being used as a shorthand for "uncommonly good" or "uncommonly well", and being repeated often by the same character as a quirk of her speech.