Old English dead "dead," also "torpid, dull;" of water, "still, standing," from Proto-Germanic *dauthaz (cf. Old Saxon dod, Danish død, Swedish död, Old Frisian dad, Middle Dutch doot, Dutch dood, Old High German tot, German tot, Old Norse dauðr, Gothic dauþs "dead"), from PIE *dhou-toz-, from root *dheu- (3) "to die" (see die (v.)).
Meaning "insensible" is first attested early 13c. Of places, "inactive, dull," from 1580s. Used from 16c. in adjectival sense of "utter, absolute, quite" (cf. dead drunk first attested 1590s; dead heat, 1796). As an adverb, from late 14c. Dead on is 1889, from marksmanship. Dead duck is from 1844. Dead letter is from 1703, used of laws lacking force as well as uncollected mail. Phrase in the dead of the night first recorded 1540s.
For but ich haue bote of mi bale I am ded as dorenail (c.1350).Dead soldier "emptied liquor bottle" is from 1913 in that form; the image is older:
Dead man, or Dead marine, a colloquialism for an empty bottle, possibly in humorous recognition of the fact that the spirits have departed. But the French also have the same phrase, un corps mort, a dead body, for which there can be no punning pretext. [Walsh, 1892]
Having lost life; no longer alive.
Lacking feeling or sensitivity; unresponsive.
With no possibility of escape or evasion; in flagrante delicto; red-handed: was caught ''dead to rights'' and now languishes in the city Bastille (1859+)
Extremely; very much: I'm dead broke/ dead set against it (1589+)
A letter or package that can neither be delivered nor returned •Dead letter in this sense is attested from 1703 (1950s+ Post office)
[the sense ''absolute, assured, certain'' probably developed fr expressions like Middle English ded oppressed, ''completely overcome,'' 16th-century dead drunk, and others suggesting the inertness of death; when inertness suggested fixedness, unchangingness, certainty, etc, the term took on these present senses]