is,
Riches; wealth; or the god of riches.
Webster's 1828
American Dictionary of the English Language

No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.
Matthew 6:24

Mammonist
A mammonist is a person devoted to the acquisition of wealth; one whose affections are placed supremely on riches; a worldling.
Webster's 1828