What does "the dog days of summer" mean — and why is it funny?

informal

Meaning

The hottest, most sluggish stretch of the summer.

Where it comes from

It comes from the ancient Romans, who linked the summer heat to Sirius, the 'Dog Star', rising together with the sun.

Why it is funny

The mild humor is the lazy image the name now suggests. Most people picture not a star at all but a hot, flattened dog lying in the shade, far too overheated to move — which fits the season perfectly.

Used in a sentence

"Nothing much gets done in the office during the dog days of summer."