What does "stare" mean?

1. (to look fixedly) to look at someone or something for a long time with your eyes wide open. 2. (a long look) a long, steady look at someone or something.

Is it correct to say "It is rude to stare someone."?

No — say "It is rude to stare at someone.". The verb 'stare' requires the preposition 'at' when followed by an object.

stare

v. · n.

US //ˈstɛɹ// UK //stˈeə// stare

1 to look fixedly (v.)
B1 Intermediate

to look at someone or something for a long time with your eyes wide open.

to gaze fixedly and intently, often with wide-open eyes. Intransitive, typically taking the preposition 'at'.

Example

The little boy started to stare at the man's colorful hat.

Example

She continued to stare at the horizon long after the ship had disappeared, lost in a profound sense of melancholy.
Pitfall

It is rude to stare someone.

It is rude to stare at someone.

The verb 'stare' requires the preposition 'at' when followed by an object.
2 a long look (n.)
B2 Upper Intermediate

a long, steady look at someone or something.

a fixed, persistent, or intent look.

Example

He gave her a long, cold stare that made her feel uncomfortable.

Example

The professor met the student's excuse with a skeptical stare, waiting for a more plausible explanation for the missing assignment.
- gaze
- glare
- glance

Etymology 1

From Middle English staren, from Old English starian (“to stare”), from Proto-West Germanic starēn, from Proto-Germanic starjaną, starāną (“to be fixed, be rigid”), from Proto-Indo-European ster-. Cognate with Dutch staren (“to stare”), German starren (“to stare”), German starr (“stiff”). More at start.

Etymology 2

From Middle English star, ster, from Old English stær (“starling”), from Proto-Germanic starô (“starling”), from Proto-Indo-European stor- (“starling”). Cognate with German Star (“starling”), Danish stær (“starling”), Swedish stare (“starling”), Norwegian Nynorsk stare (“starling”), Icelandic stari (“starling”). Compare also Old English stearn (“a type of bird, starling”).