cross (n.) Look up cross at Dictionary.com
Old English cros "instrument of Christ's crucifixion; symbol of Christianity" (mid-10c.), from Old Irish cros, probably via Scandinavian, from Latin crux (accusative crucem, genitive crucis) "stake, cross" on which criminals were impaled or hanged (originally a tall, round pole); hence, figuratively, "torture, trouble, misery." The word is possibly of Phoenician origin. Replaced Old English rood.

Also from Latin crux are Italian croce, French croix, Spanish and Portuguese cruz, Dutch kruis, German Kreuz.

By c.1200 as "ornamental likeness of the cross, something resembling or in the form of a cross; sign of the cross made with the right hand or with fingers." From mid-14c. as "small cross with a human figure attached; a crucifix;" late 14c. as "outdoor structure or monument in the form of a cross." Also late 14c. as "a cross formed by two lines drawn or cut on a surface; two lines intersecting at right angles; the shape of a cross without regard to religious signification." From late 12c. as a surname.

From c.1200 in the figurative sense "the burden of a Christian; suffering; a trial or affliction; penance in Christ's name," from Matt. x.38, xvi.24, etc. Theological sense "crucifixion and death of Christ as a necessary part of his mission" is from late 14c.

As "a mixing of breeds in the production of animals" from 1760, hence broadly "a mixture of the characteristics of two different things." In pugilism, 1906, from the motion of the blow (1880s as a verb; cross-counter (n.) is from 1883).
cross (adj.) Look up cross at Dictionary.com
developed in early Modern English from the adverb (see cross (adv.)). Earliest sense is "falling athwart, lying athwart the main direction" (1520s). Meaning "intersecting, lying athwart each other" is from c.1600.

Sense of "adverse, opposed, contrary, opposite" is from 1560s; of persons, "peevish, ill-tempered," from 1630s, probably from the earlier senses of "contrary, athwart," especially with reference to winds and sailing ships. A 19c. emphatic form was cross as two sticks (1807), punning on the verb.

Cross-purposes "contradictory intentions" is from 1660s. Cross-legged is from 1520s; cross-grained is from 1670s of wood; as "opposed in nature or temper" from 1640s.
cross (v.) Look up cross at Dictionary.com
c.1200, "make the sign of a cross," from cross (n.) and in part from French croiser. Sense of "to go across, pass from side to side of, pass over" is from c.1400; that of "to cancel by drawing crossed lines over" is from mid-15c.

From late 14c. as "lie across; intersect;" also "place (two things) crosswise of each other; lay one thing across another." From early 15c. as "mark a cross on." Also in Middle English in now-archaic sense "crucify" (mid-14c.), hence, figuratively, crossed "carrying a cross of affliction or penance." Meaning "thwart, obstruct, hinder, oppose" is from 1550s; that of "cause to interbreed" is from 1754. In telegraphy, electricity, etc., in reference to accidental contact of two wires on different circuits or different parts of a circuit that allows part of the current to flow from one to the other, from 1884. Meaning "to cheat" is by 1823.

Cross my heart as a vow is from 1898. To cross over as euphemistic for "to die" is from 1930. To cross (someone's) path is from 1818. Of ideas, etc., to cross (someone's) mind is from 1768; the notion is of something entering the mind as if passing athwart it. Related: Crossed; crossing.
cross (adv.) Look up cross at Dictionary.com
c.1400, "to the side," from on cros, variant of across.