Swear \Swear\, v. i. [imp. Swore, formerly Sware; p. p. Sworn; p. pr. & vb. n. Swearing.]

[OE. swerien, AS. swerian; akin to D. zweren, OS. swerian, OHG. swerien, G. schw["o]ren, Icel. sverja, Sw. sv["a]rja, Dan. sv[ae]rge, Icel. & Sw. svara to answer, Dan. svare, Dan. & Sw. svar an answer, Goth. swaran to swear, and perhaps to E. swarm. [root]177. Cf. Answer.]

1. To affirm or utter a solemn declaration, with an appeal to God for the truth of what is affirmed; to make a promise, threat, or resolve on oath; also, to affirm solemnly by some sacred object, or one regarded as sacred, as the Bible, the Koran, etc.

Ye shall swear by my name falsely. --Lev. xix. 12.

I swear by all the Roman gods. --Shak.

2. (Law) To give evidence on oath; as, to swear to the truth of a statement; he swore against the prisoner.

3. To make an appeal to God in an irreverant manner; to use the name of God or sacred things profanely; to call upon God in imprecation; to curse.

[I] swore little; diced not above seven times a week. --Shak.

To swear by, to place great confidence in a person or thing; to trust implicitly as an authority. ``I simply meant to ask if you are one of those who swear by Lord Verulam.'' --Miss Edgeworth.

To swear off, to make a solemn vow, or a serious resolution, to abstain from something; as, to swear off smoking. [Slang]

Source: Webster's Revised Unabridged Dictionary (1913)
 

Sworn \Sworn\, p. p. of Swear.

Sworn brothers, originally, companions in arms who took an oath to share together good and bad fortune; hence, faithful friends.

Sworn enemies, determined or irreconcilable enemies.

Sworn friends, close friends.

Source: Webster's Revised Unabridged Dictionary (1913)