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 Norse sverja, Danish sverge, Old Frisian swera, 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"). Also related to the second element in answer. The secondary sense of "use bad language" (early 15c.) developed from the notion of "invoke sacred names." Swear-word is American English colloquial from 1883. Swear off "desist as with a vow" is from 1898.
A police unit wearing military-like uniforms and using military assault weapons on assignments requiring extraordinary coordination and force: When the terrorists took over the whole building, the commissioner sent in the SWAT team
[1969+; fr acronym of special weapons and tactics used as a modifier]