Linguists propose that English Presbyterians coined the word "selfish" in the 1630s. The etymology suggests "selfish" means "about the self" in the same way that "noonish" denotes "around noon." In its etymological and historical origins, "selfish" is a pejorative term used to describe someone who disregards the needs and interests of others.

According to the Merriam-Webster dictionary, the contemporary use of the word denotes two characteristics:

1. Concerned excessively or exclusively with oneself: seeking or concentrating on one's own advantage, pleasure, or well-being without regard for others.

2. Arising from concern with one's own welfare or advantage in disregard of others (a selfish act).

An assessment of "selfishness" based on the 16 Personality Factors Theory of the renowned British psychologist Raymond Cattell reveals that some characteristics of selfishness can include the following:

A low score on the Warmth scale, indicating traits such as being impersonal, distant, cool, reserved, detached, formal and aloof.

A high score on the Dominance scale, indicating traits such as being dominant, forceful, assertive, aggressive, competitive, stubborn and bossy.

A low score on the Liveliness scale, indicating traits such as being serious, restrained, prudent, taciturn, introspective and silent.

A low score on the Social Conscientiousness scale, indicating traits such as being expedient, nonconforming, self-indulgent and disregarding of rules.

A high score on the Vigilance scale, indicating traits such as being vigilant, suspicious, skeptical, distrustful and oppositional.

A high score on the Privateness scale, indicating traits such as being private, discreet, nondisclosing, shrewd, polished, worldly, astute and diplomatic.

A high score on the Self-Reliance scale, indicating traits such as being self-reliant, solitary, resourceful, individualistic and self-sufficient.

A high score on the Perfectionism scale, indicating traits such as being perfectionist, organized, compulsive, self-disciplined, socially precise and self-sentimental, and exercising will power and control.

According to evolutionary psychologists, self-serving interests in survivability and reproduction primarily drive organisms. In social dynamics with other organisms, selfishness is often seen as a quality that is damaging for the group. Evolutionary psychologist Nicholas Humphrey has proposed that social animals, including humans, demonstrate "Machiavellian Intelligence" that masks selfishness as altruism. For example, the act of helping another person appears to be altruistic, but it is actually an act of self-interest. By helping others in a group, the individual increases their chances of being helped by the group. The apparent act of altruism is actually an act of selfishness known as reciprocal altruism.