Synonym Boundary: "いち", "一", "一つ", "億", "いちいち"

When expressing "one" in Japanese, you must carefully distinguish between "いち", "一", "一つ", "億", "いちいち" based on context.

• いち (いち (ichi) - Level: N5): Maps to "one" and is used when Basic number for counting. Can be used as a standalone number or with various counters.
• 一 (いち (ichi) - Level: N5): Maps to "one" and is used when 数を数えるときに使います。ひとつ、一人、一日など、他の言葉と組み合わせて使われることも多いです。/ Used for counting. Often combined with other words like 'hitotsu'.
• 一つ (ひとつ (hitotsu) - Level: N5): Maps to "one (general counter for objects)" and is used when Used for counting general items, especially small, individual objects, when a specific counter is not needed or known..
• 億 (おく (oku) - Level: N3): Maps to "one hundred million (100,000,000)" and is used when A large numerical unit in Japanese. 1億 = 100,000,000. Often used for large amounts of money, population, or astronomical figures..
• いちいち (いちいち (ichiichi) - Level: N2): Maps to "one by one; in detail; item by item; minutely; every single time (often implies annoyance or unnecessary thoroughness)" and is used when Implies going through things individually or paying attention to every small detail. Can convey a sense of annoyance when someone is being excessively meticulous or complaining about every little thing..

Mixing these up can easily lead to unnatural translations. Refer to the bilingual context cards below to master the boundaries!