Dai-ichi (第一) is a compound modifier phrase of Japanese origin, meaning number one, or first. In kanji, "dai" ("number") is 第 and "ichi" ("one") is 一. "Dai" is also defined "ordinal number marker." It is this feature that makes the phrase a modifier, or an adjective, describing a noun, as first. Number one functions in the same way.

The phrase is also written without the hyphen, as daiichi.

Dai-ichi is frequently used in proper names, hence capitalized; also Dai-Ichi and occasionally Dai Ichi. There is a sound-alike common first name with different spelling.

Dai-ni (第二) means number two or second, using two parallel bars (二) or "2" for "ni"; also daini

Dai-san (第三) means number three or third, using three parallel bars (三) or "3" for "san"

And continuing for 4, 5, 6, etc.