To come down from one's superior position; to deign (to do something).

To treat (someone) as though inferior; to be patronizing (toward someone); to talk down (to someone).

(possibly nonstandard) To treat (someone) as though inferior; to be patronizing toward (someone); to talk down to (someone).

Assuming a tone of superiority, or a patronizing attitude.

“Quit talking to me in that condescending tone! You always treat me like a child!”