What is the meaning of Nay?

Introducing a statement, without direct negation.

Or rather, or should I say; moreover (introducing a stronger and more appropriate expression than the preceding one).

A vote against.

A person who voted against.

Nary; not any

my younger sibling; used to address a sibling of the speaker who is younger than the speaker and of the same sex

Clipping of nanay.

that is today, or happening today

now, the present, as opposed to xưa (“long ago; the past”) and mai (“later in the future”)

Clipping of hôm nay (“today”)

Clipping of bữa nay (“today”)

Source: wiktionary.org

See also