My definition of "Yeet" is to fling/throw/hurl something, typically with great vigor. Urban Dictionary defines it as "To discard an item at a high velocity." Derives from the Latin Iacio, From Proto-Italic jakjō, from Proto-Indo-European (H)yeh₁- ("to throw, let go"). JK I just made that up, but it's actually plausible.
Never heard the "exclamation of excitement" definition.