Webster's Revised Unabridged Dictionary · 1913

gotta

gotta (got"tu) , phrase

[phonetic transcription of colloquial speech, from got to.]

Got to; have to; must; as, I gotta leave now. [colloquial, phonetic spelling]

Phonetic transcriptions of rapid colloquial speech are sometimes used in place of the grammatically proper spelling in order to provide a flavor of the original spirit of a spoken dialogue. See also the related entries for gonna, wanna, and wannabe.