Learn English – Introductory word meaning “considering what was previously said”

I feel compelled to correct my spelling after StoneyB's answer. The correct spelling is discreet, not discrete.

Discreet here means using discretion, respecting issues of privacy and decency.

Having a word with someone means having a talk with them.

Having a discreet word with someone usually means you talk to someone in private - you take them apart at the coffee corner, or you move into a meeting room. It indicates the opposite of giving someone a public telling off. It is often considered unkind to criticize someone in public, in front of their friends or colleagues. Having a discreet word with them, you make sure they do get the message,but it is not a public event.

It's not a pronoun because it doesn't take the place of a noun - not by itself anyway. No one/nobody/nothing/nowhere would be some of the "pronoun forms" of no.

No generally modifies a noun so that makes it technically an adjective. When modifying a verb or adjective not is used.

No is also a typically a determiner - which can be considered a special type of adjective - because it can occupy the "spot" where an article or word like this/that/these/those would go.