IPA: /ˈskiːmər/
KK: /ˈskimɚ/
A person who makes secret plans or plots, often for dishonest or selfish reasons.
The schemer devised a clever plan to trick his friends.
Schemer → It is formed from "scheme" (from Greek "schēma", meaning form or plan) and "-er" (meaning a person who). A schemer is a person who devises plans or plots, often with a connotation of cunning or deceit.
Think of someone who creates a 'plan' ('scheme') — the '-er' indicates that this person is actively involved in making those plans.