彼氏(かれし)

ETYMOLOGY: 彼(かれ) (he) + 氏(し) (honorific suffix). The 氏(し) suffix adds a slight formal/distancing nuance, but the word itself is casual.

CONTRAST:

• 彼氏(かれし) ↔ 彼女(かのじょ) (boyfriend ↔ girlfriend)
• Both are standard casual terms for romantic partners

FORMAL/OTHER EXPRESSIONS:

• 恋人(こいびと) (lover, sweetheart - gender-neutral, slightly formal)
• パートナー (partner - modern, gender-neutral)
• お付(つ)き合(あ)いしている人(ひと) (person I'm dating - polite)
• 交際(こうさい)相手(あいて) (dating partner - formal)

COMMON COLLOCATIONS:

• 彼氏(かれし)ができる (to get a boyfriend)
• 彼氏(かれし)と別(わか)れる (to break up with one's boyfriend)
• 彼氏(かれし)と付(つ)き合(あ)う (to date one's boyfriend)
• 彼氏(かれし)がいる (to have a boyfriend)
• 彼氏(かれし)を紹介(しょうかい)する (to introduce one's boyfriend)

USAGE NOTE:
彼氏(かれし) is the most common casual term for "boyfriend" in everyday conversation. The term 彼(かれ) alone can also mean "boyfriend" in context, often used when the relationship is already understood.