The difference between Refuse and Say no

When used as verbs, refuse means to decline (a request or demand), whereas say no means to disagree.

Refuse is also noun with the meaning: collectively, items or material that have been discarded.

Refuse is also adjective with the meaning: discarded, rejected.

check bellow for the other definitions of Refuse and Say no

Refuse as a noun:

Collectively, items or material that have been discarded; rubbish, garbage.

Refuse as a verb (transitive):

To decline (a request or demand).

Examples:

"My request for a pay rise was refused."
Refuse as a verb (intransitive):

To decline a request or demand, forbear; to withhold permission.

Examples:

"I refuse to listen to this nonsense any more."

"I asked the star if I could have her autograph, but she refused."
Refuse as a verb (military):

To throw back, or cause to keep back (as the centre, a wing, or a flank), out of the regular alignment when troops are about to engage the enemy.

Examples:

"to refuse the right wing while the left wing attacks"
Refuse as a verb (obsolete, transitive):

To disown.

Say no as a verb:

To disagree; to think something or someone is doing or saying what is wrong.
Say no as a verb:

To reject something.

Examples:

"Just say no to drugs."