What is the meaning of Nullo?

A bid in which the bidder asserts that he or she will not take any tricks.

One who has their genitals (and sometimes nipples) surgically removed (nullification) as a form of body modification.

no, not any

futile, ineffectual, vain

null; equating zero

null, null and void

no one, nobody

ablative masculine/neuter singular of nūllus

ablative masculine/neuter singular of nūllus

Source: wiktionary.org