Gonna
来自Big Physics
early 19th century (as ganna ): representing a regional or colloquial pronunciation.
wiktionary
Written form of a reduction of going to. Attested since 1917. The pronunciation of present participles with the sound n rather than ng has a long history (see g-dropping on Wikipedia).
etymonline
gonna
attempt to represent the casual pronunciation of going to. In Scottish dialect, ganna, gaunna recorded from 1806.
