그이 means "he", like 그, but has two usages. 1) plain "he" to refer to someone already mentioned. No special nuance here. 2) an affectionate "the one" or "my beloved one" used by women referring to her husband or sweetheart as a third person ex) 우리 그이가 말하는데...: My husband told me... For #1) it might be confusing because there is already "그" with the same thing. My understanding is that 그이 is a traditional Korean word used since hundreds of years ago referring to a man. In modern times (around the turn of 20th century) new words for 그 and 그녀 came into Korean to mean he / she (or it could have been from Japan - not sure). These new words 그/ 그녀 really don't jibe with the Korean words that much phonetically, so as far as I know they are still not used much in everyday conversation. They are heavily used in writings and some formal speeches, but in daily life most people say 그 애 (걔), 그사람, or 그이 for "he", and 그 여자애 or 그 여자 for "she" depending on their age and the social setting. Anyway, like 그, 그이 is not used that much in speech because 그사람 is so prevalent. I think at least part of the reason is that its sound doesn't stand out like 그사람 when you speak fast because it ends with 이 which has no consonant.