OP, let me introduce you to Wiktionary, where you can look up all sorts of words, "gravity" included.

It can be a little shaky around the fringes (obscure words; rare or slang usages) and with languages not closely related to English, but it's an excellent resource for when you want to know why a word is the way it is. Or at least to find out that we don't know for sure where some words come from. Gravity isn't one of those, though.

You may also like to know that there is a metric physical unit named after Newton, so his name does get used in gravity-related concepts. At time of writing, the Wikipedia article for the Gravity of Earth mentions the unit in the first couple of paragraphs.