Overdraft

Etymology

A compound of "over" + "draft", where "draft" comes from "draw" — drawing out funds. To overdraw is to draw out more than is there, and the resulting shortfall is the overdraft. The banking sense simply extends the everyday idea of drawing water or money beyond the supply.

noun · /OH-vur-draft/
A negative balance that occurs when you spend more money than your account holds, often triggering a fee.
What it names
The moment an account goes below zero — a small, usually expensive form of automatic borrowing that catches people unaware.
Example
One mistimed payment tipped the account into overdraft and cost him a $35 fee overnight.
Related idea
Distinguish it from insufficient-funds rejection: with overdraft coverage the bank lets the payment go through and charges you, whereas without it the payment simply bounces — different failures with different fees.