What does "hold your horses" mean — and why is it funny?

informal

Meaning

Wait; slow down; do not be so hasty.

Where it comes from

An American phrase from the 1800s, from the literal act of reining in horses to halt a cart or carriage.

Why it is funny

The humor now is that almost no one saying it has any horses. Telling a hurried person in a modern office to 'hold your horses' hands them the reins of animals that are not there, which makes the urgency sound faintly ridiculous.

Used in a sentence

"Hold your horses — let me finish my coffee before we leave."