Answer for

a spoken or written reply or response to a question, request, letter, etc.:
He sent an answer to my letter promptly.
a correct response to a question asked to test one’s knowledge.
an equivalent or approximation:
a singing group that tried to be the French answer to the Beatles.
an action serving as a reply or response:
The answer was a volley of fire.
a solution to a problem, especially in mathematics.
a reply to a charge or accusation.
Law. a pleading in which a party responds to his or her opponent’s statement of position, especially the defendant’s reply to the plaintiff’s complaint.
Music. the entrance of a fugue subject, usually on the dominant, either slightly altered or transposed exactly after each presentation in the tonic.
to speak or write in response; make answer; reply.
to respond by an act or motion:
He answered with a nod. The champion answered with a right to the jaw.
to act or suffer in consequence of (usually followed by for).
to be or declare oneself responsible or accountable (usually followed by for):
I will answer for his safety.
to be satisfactory or serve (usually followed by for):
His cane answered for a baseball bat.
to conform; correspond (usually followed by to):
The prisoner answered to the description issued by the police.
to speak or write in response to; reply to:
to answer a person; to answer a question.
to act or move in response to:
Answer the doorbell. We answered their goal with two quick goals of our own.
to solve or present a solution of.
to serve or fulfill:
This will answer the purpose.
to discharge (a responsibility, claim, debt, etc.).
to conform or correspond to; be similar or equivalent to:
This dog answers your description.
to atone for; make amends for.
to reply or respond favorably to:
I would like to answer your request but am unable to do so.
answer back, to reply impertinently or rudely:
Well-behaved children do not answer back when scolded.
answer the helm, Nautical. (of a vessel) to maneuver or remain steady according to the position of the rudder.
verb (intransitive, preposition)
to be liable or responsible for (a person’s actions, behaviour, etc)
to vouch for or speak on behalf of (a person)
to suffer or atone for (one’s wrongdoing)
noun
a reply, either spoken or written, as to a question, request, letter, or article
a reaction or response in the form of an action: drunkenness was his answer to disappointment
a solution, esp of a mathematical problem
(law)

a party’s written reply to his opponent’s interrogatories
(in divorce law) the respondent’s written reply to the petition

a musical phrase that follows the subject of a fugue, reproducing it a fifth higher or a fourth lower
verb
(when transitive, may take a clause as object) to reply or respond (to) by word or act: to answer a question, he answered, to answer the door, he answered that he would come
(transitive) to reply correctly to; solve or attempt to solve: I could answer only three questions
(intransitive) usually foll by to. to respond or react (to a stimulus, command, etc): the steering answers to the slightest touch
(transitive) to pay off (a debt, obligation, etc); discharge
when intr, often foll by for. to meet the requirements (of); be satisfactory (for); serve the purpose (of): this will answer his needs, this will answer for a chisel
when intr, often foll by to. to match or correspond (esp in the phrase answer (or answer to) the description)
(transitive) to give a defence or refutation of (a charge) or in (an argument)
n.

Old English andswaru “an answer, a reply,” from and- “against” (see ante) + -swaru “affirmation,” from swerian “to swear” (see swear), suggesting an original sense of “make a sworn statement rebutting a charge.” A common Germanic compound (cf. Old Saxon antswor, Old Norse andsvar, Old Frisian ondser, Danish and Swedish ansvar), implying a Proto-Germanic *andswara-. Meaning “a reply to a question,” the main modern sense, was present in Old English. Meaning “solution of a problem” is from c.1300.
v.

Old English answarian “to answer;” see answer (n.). Meaning “to respond in antiphony” is from early 15c.; that of “to be responsible for” is early 13c. Related: Answered; answering. The telephone answering machine is from 1961.
Take responsibility for, take charge of, as in The new alarm system has to answer for the security of the grounds. [ Late 1200s ]
Take the blame for, as in The kids who were caught shoplifting have a lot to answer for. [ c. 1200 ]
To vouch for or sponsor someone, as in I’ll answer for John as a reliable employee. [ Early 1700s ]

answer back
answer for
answer to

also see:

know all the answers
take no for an answer