is the Old English and-swaru, verb and swar-ian or swerian, where And is the preposition = the Latin re in re-spond-eo. (See Swear.)
“We say, in France. ‘Answering like a Norman,’ which means to give an evasive answer, neither yes nor no.” —Max O'Rell; Friend M Donald, ch. v.
In both the last two instances the word is “answering to a summons.”
To swear means literally “to affirm something,” and to an-swear is to “say something” by way of rejoinder; but figuratively both the “swer” and the “answer” may be made without words.
... My story being done, ... She [Desdemona ] swore [affirmed ] 'twas strange,... 'Twas pitiful, 'twas wondrous pitiful.
Shakespeare: Othello, i. 3.