The pronunciation of the Sino-Korean number “one” and the noun “work” sound that same, but the length is different.
- 일 [일] – short and sharp
- 일 [일:] – a bit longer
If you mean the ordinal number one, say “일 번 [일번]” with a strong pitch accent right at the start. But if you make it flat or drag it out like “일 번 [일:번],” it sounds unnatural. That’s like mixing up live and leave in English.
Now, if you mean “work,” it should be “일 [일:],” a little longer.
- 일이 많아요. [이:리 마나요] – I have a lot of work to do.
- 일이 많아요. [이리 마나요] – I have many number ones.
And that’s pretty much the only big one you should really distinguish. There aren’t many words in Korean where vowel length changes the meaning this much.
Actually, there’re few more: the Sino-Korean number “two” and “four” are also long.
So, when you do the Sino-Korean numbers: 1 [일], 2 [이:], 3 [삼], 4 [사:], 5 [오], 6 [육], 7 [칠], 8 [팔], 9 [구], 10 [십], 11 [십일 or 시빌], 12 [십이: or 시비:], 13 [십삼 or 십쌈], 14 [십사:]…
Now that’s really it.