To swear – etymology

If we swear by the SUN of beloved person and lie,

that belover person will not sea sun anymore, will die

Oath in Old English að “oath, judicial swearing, solemn appeal to deity in witness of truth or a promise,” from Proto-Germanic *aithaz (cf. Old Norse eiðr, Swedish ed, Old Saxon, Old Frisian eth, Middle Dutch eet, Dutch eed, German eid, Gothic aiþs “oath”), from PIE *oi-to- “an oath” (cf. Old Irish oeth “oath”). In reference to careless invocations of divinity, from late 12c.

Swear in Old English swerian “take an oath” (class VI strong verb; past tense swor, past participle sworen), from Proto-Germanic swarjan-, (cf. Old Saxon swerian, Old Frisian swera, Old Norse sverja, Danish sverge, Middle Dutch swaren, Old High German swerien, German schwören, Gothic swaren “to swear”), from PIE root *swer- (1) “to speak, talk, say” (cf. Old Church Slavonic svara “quarrel,” Oscan sverrunei “to the speaker”).

Also related to the second element in answear. The secondary sense of “use bad language” (early 15c.) developed from the notion of “invoke sacred names.” Swear off “desist as with a vow” is from 1898. Swear in “install in office by administration of an oath” is from 1700 in modern use, echoing Old English.

Old English andswaru “an answer, a reply,” from and- “against” (ante + -swaru “affirmation,” from swerian “to swear”, suggesting an original sense of “make a sworn statement rebutting a charge.”

A common Germanic compound (cf. Old Saxon antswor, Old Norse andsvar, Old Frisian ondser, Danish and Swedish ansvar), implying a Proto-Germanic andswara-. Meaning “a reply to a question,” the main modern sense, was present in Old English. Meaning “solution of a problem” is from c.1300.