Select the option that can be used as a one-word substitute for the given…

Concept

A one-word substitute condenses a descriptive phrase into one term without changing its core meaning. For descriptions of people, compare the relationship expressed—authority, equality, grouping, or companionship.

Application

The phrase describes a person on equal standing in rank, merit, or quality. Peer denotes a person of the same rank, status, or ability, so it supplies the required single word.

Contrast

• Leader denotes someone who guides or directs a group, emphasizing authority rather than equal standing.

• Pair denotes two corresponding people or things considered together, emphasizing grouping rather than rank.

• Friend denotes someone joined to another by affection or trust, emphasizing companionship rather than equality of rank.

Cross-check

Replacing the phrase in 'a person equal in rank to another' with peer preserves the meaning: 'a peer of another person.' Therefore, the one-word substitute is peer.