One Word Substitution

To acquaint means to make someone aware of or familiar with something. The other options are adjectives describing negative qualities.

Acrimonious describes a speech or debate that is angry and bitter. The other options are unrelated.

Acumen is the ability to make good judgments and quick decisions, typically in a particular domain. Acuter is just a comparative adjective.

Adamant refers to refusing to be persuaded or to change one's mind. The other options are unrelated.

Adonis is a term used to describe a very handsome young man, derived from Greek mythology. The other options are unrelated.

Aetiology (or etiology) is the study of the causes, origins, or reasons behind diseases. The other options are nonsense words or unrelated fields.

An agnostic is a person who believes that nothing is known or can be known of the existence or nature of God. The other options are unrelated.

A person who walks in their sleep is a somnambulist. Somna = sleep, ambulate = walk. Hence, a somnambulist is a person who walks in their sleep.

Ans-4

Celibacy is the state of being unmarried, often associated with religious vows, though it generally refers to the state of not being married.

A glutton is a person who eats and drinks excessively.

A sexton is an officer of a church who is in charge of the maintenance of the church buildings and grounds.

A pessimist is someone who tends to see the worst aspect of things or believes that the worst will happen.

An ambidexter (or ambidextrous person) is someone who can use both hands with equal ease.

An inferno is a large fire that is dangerously out of control, often used metaphorically to describe a place like hell.