Nab? Grab? Connection? Etymology?

Can anybody tell me about the connection, if any, between the words nab and grab.

It struck me that the a/b ending is unusual.

Do they have a common origin?

Yeah – aside from cab, crab, dab, drab, gab, jab, scarab, stab, (swab), and tab, and, oh, shortenings like lab and fab – and, of course, Queen Mab – you hardly ever see it.

[Origin uncertain; perh. variant of NAP v.3]

1. trans.    a. To catch (a criminal, etc.) and take into custody; to apprehend, arrest; to imprison. 

1686 F. SPENCE tr. A. Varillas Secret Hist. House Medicis 407 Verselli was nabb’d playing at dice.

At Nap ,they offer the etymology as

Grab also goes back to this time period, but appears to have nothing in common with nab

Scab. Slab. Flab.