From Wiktionary, the free dictionary
Compound of だ ( da , the plain-form copula or "to be" verb ) + い ( emphatic particle , used in compounds with certain sentence-ending particles to create a familiar effect) .[ 1] [ 2]
Attested since at least 1809.[ 1]
だい • (dai )
[from 1908] ( informal , men's speech ) an interrogative particle
どうしたんだい ? Dō shita n dai ? What’s the matter?
[from 1809] ( dated ) a particle used to state something with conviction
そんなのはいらねえってんだい 。 Sonna no wa iranē tte n dai . I don't need that stuff.
For pronunciation and definitions of だい – see the following entries.
【第 】 3
[prefix] ordinal marker, often with affix 号
(This term, だい ( dai ) , is the hiragana spelling of the above terms.)For a list of all kanji read as だい , see Category:Japanese kanji read as だい .)