sheer (adj.)

c. 1200, "exempt, free from guilt" (as in Sheer Thursday, the Thursday of Holy Week); later schiere "thin, sparse" (c. 1400), from Old English scir "bright, clear, gleaming; translucent; pure, unmixed," and influenced by Old Norse cognate scær "bright, clean, pure," both from Proto-Germanic *skeran (source also of Old Saxon skiri, Old Frisian skire, German schier, Gothic skeirs "clean, pure"), from PIE root *sker- (1) "to cut."

Sense of "absolute, utter" (sheer nonsense) developed 1580s, probably from the notion of "unmixed;" that of "very steep" (a sheer cliff) is first recorded 1800, probably from notion of "continued without halting." Meaning "diaphanous" is from 1560s. As an adverb from c. 1600.

sheer (v.)

1620s, "deviate from course" (of a ship), of obscure origin, perhaps from Dutch scheren "to move aside, withdraw, depart," originally "to separate" (see shear (v.)). Related: Sheered; shearing. As a noun from 1660s.

Others are reading

Definitions of sheer from WordNet
sheer (adj.)
complete and without restriction or qualification; sometimes used informally as intensifiers;
got the job through sheer persistence
sheer stupidity
Synonyms: absolute / downright / out-and-out / rank / right-down
sheer (adj.)
not mixed with extraneous elements;
sheer wine
Synonyms: plain / unmingled / unmixed
sheer (adj.)
very steep; having a prominent and almost vertical front;
a sheer descent of rock
Synonyms: bluff / bold
sheer (adj.)
so thin as to transmit light;
sheer silk stockings
Synonyms: diaphanous / filmy / gauzy / gauze-like / gossamer / see-through / transparent / vaporous / vapourous / cobwebby
sheer (v.)
turn sharply; change direction abruptly;
Synonyms: swerve / curve / trend / veer / slue / slew / cut
sheer (v.)
cause to sheer;
She sheered her car around the obstacle
sheer (adv.)
straight up or down without a break;
Synonyms: perpendicularly
sheer (adv.)
he fell sheer into the water