이성

• (SK Standard/Seoul) IPA^(key): [ˈi(ː)sʰʌ̹ŋ]
• Phonetic hangul: [이(ː)성]
  • Though still prescribed in Standard Korean, most speakers in both Koreas no longer distinguish vowel length.

Sino-Korean word from 異性, from 異 (“different”) + 性 (“gender; sex”)

이성 • (iseong) (hanja 異性)

1. opposite sex

• 동성 (同性, dongseong, “same sex)”)

• 이성애 (異性愛, iseong'ae, “heterosexuality”)

 

Korean Wikipedia has an article on:

이성

Wikipedia ^ko

Sino-Korean word from 理性

이성 • (iseong) (hanja 理性)

1. (philosophy, South Korea) reason; logic; rationality

• 리성 (理性, riseong) (North Korea, Yanbian dialect)

• 이유 (理由, iyu, “reason; cause”)