What's the "een" in Halloween?
"to make snowballs," 1680s, from snowball (n.); sense of "to throw snowballs at" (someone) is from 1850. Meaning "to increase rapidly" is attested from 1929, though the image of a snowball increasing in size as it rolls along had been used since at least 1613, and a noun sense of "a pyramid scheme" is attested from 1892. Related: Snowballed; snowballing.
[first sense fr the fact that a snowball rolled downhill becomes larger and larger; second sense fr the notion of attacking someone with snowballs]