eyeball n.

c. 1200, from Old English ege (Mercian), eage (West Saxon) "eye; region around the eye; apperture, hole," from Proto-Germanic *augon (source also of Old Saxon aga, Old Frisian age, Old Norse auga, Swedish öga, Danish øie, Middle Dutch oghe, Dutch oog, Old High German ouga, German Auge, Gothic augo "eye"). Apparently the Germanic form evolved irregularly from PIE root *okw- "to see."

HAMLET: My father — methinks I see my father.

HORATIO: Where, my lord?

HAMLET: In my mind's eye, Horatio.

Until late 14c. the English plural was in -an, hence modern dialectal plural een, ene. Of potatoes from 1670s. Of peacock feathers from late 14c. As a loop used with a hook in fastening (clothes, etc.) from 1590s. The eye of a needle was in Old English. As "the center of revolution" of anything from 1760. Nautical in the wind's eye "in the direction of the wind" is from 1560s.

To see eye to eye is from Isaiah lii.8. Eye contact attested from 1953. To have (or keep) an eye on "keep under supervision" is attested from early 15c. To have eyes for "be interested in or attracted to" is from 1736; make eyes at in the romance sense is from 1837; gleam in (someone's) eye (n.) "barely formed idea" is from 1959. Eye-biter was an old name for "a sort of witch who bewitches with the eyes."

"round object, compact spherical body," also "a ball used in a game," c. 1200, probably from an unrecorded Old English *beal, *beall (evidenced by the diminutive bealluc "testicle"), or from cognate Old Norse bollr "ball," from Proto-Germanic *balluz (source also of Dutch bal, Flemish bal, Old High German ballo, German Ball), from PIE root *bhel- (2) "to blow, swell."

The meaning "testicle" is from early 14c. (compare ballocks). Ball of the foot is from mid-14c. The meaning "rounded missile used in warfare" is from late 14c.

The meaning "a game played with a ball" is from mid-14c. The baseball sense of "pitch that does not cross the plate within the strike zone" is by 1889, probably short for high ball, low ball, etc.

Ball-point pen is by 1946. Ball of fire when first recorded in 1821 referred to "a glass of brandy;" as "spectacularly successful striver" it is attested from c. 1900. Many phrases are from sports: To have the ball "hold the advantage" is from c. 1400. To be on the ball is from 1912; to keep (one's) eye on the ball in the figurative sense is by 1907, probably ultimately on golf, where it was oft-repeated advice. Figurative use of ball in (someone's) court is by 1956, from tennis.

The head must necessarily be steady, for it is most important that you should keep your eye fixedly on the ball from the moment that the club-head is lifted from the ground until the ball is actually struck. "Keep your eye on the ball," should be your companion text to "Slow back." [Horace G. Hutchinson, "Hints on the Game of Golf," 1886]

Once a meeting is over, someone will be expected to do something. Make sure it is someone else. This is known as keeping the ball in their court. [Shepherd Mead, "How to Get Rich in TV Without Really Trying," 1956]