Selfish means putting yourself first and not caring what it costs anyone else. The person who takes the last slice without offering it round, or parks across two spaces because it saves them a bit of reversing.
Selfish is an accusation, not a description; you do not call someone selfish and expect them to smile back. The adverb is selfishly and the noun is selfishness. There is a milder use where selfish means simply personal: I am asking for selfish reasons, I want you at the party. Self-centred sits close by, but self-centred is about where a person's attention points, while selfish is about what their actions cost other people. Biology took the word for a famous phrase, the selfish gene, where nobody is accusing the gene of anything.
1adjectiveselfishCaring only about your own wants and not about other people.
“It was a selfish thing to do and he knew it before he had finished doing it.”
synonyms: self-centred, inconsiderate
2adjectivedoneDone for your own benefit rather than anyone else's.
“I have a selfish reason for wanting you to stay: I hate driving home alone.”
Too few real examples of this word to estimate which sense is commonest.
Selfish is self with -ish stuck on the end, the same ending as childish and foolish, which tells you the tone the word was born with. Danish selvisk and Swedish självisk are built from exactly the same two pieces.
Middle English
self
English
self
English, today
selfish
From self + -ish. Compare Danish selvisk (“selfish”), Swedish självisk (“selfish”). self comes from Middle English self. From Middle English salve, self, silf, from Old English self, seolf, sylf, from Proto-Germanic selbaz, from Proto-Indo-European selbʰ- (“one's own”). 2
Etymology from Wiktionary, CC BY-SA