Eyeball

wiktionary

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From eye +‎ ball. Compare Middle English balle off the eye, balle of þe eyȝe(“eyeball”, literally “ball of the eye”).

etymonline

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eyeball (n.)

also eye-ball, "the ball or globe of the eye," so called for its shape, 1580s, from eye (n.) + ball (n.1), which is attested from c. 1400 in the sense "spherical structure of the eye." As a verb, 1901, American English slang. Related: Eyeballed; eyeballing.