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." "I swear by all the Roman gods."
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."
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