The Collaborative International Dictionary of English v.0.48:

Sware \Sware\,
   imp. of Swear. [Obs. or Poetic]
   [1913 Webster]

         Cophetua sware a royal oath.             --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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[aum]rja, Dan. svaerge,
   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.
      [1913 Webster]

            Ye shall swear by my name falsely.    --Lev. xix.
                                                  12.
      [1913 Webster]

            I swear by all the Roman gods.        --Shak.
      [1913 Webster]

   2. (Law) To give evidence on oath; as, to swear to the truth
      of a statement; he swore against the prisoner.
      [1913 Webster]

   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.
      [1913 Webster]

            [I] swore little; diced not above seven times a
            week.                                 --Shak.
      [1913 Webster]

   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]
      [1913 Webster]