Dirk is a Scots word for a long dagger; sometimes a cut-down sword blade mounted on a dagger handle, rather than a knife blade. A short dirk tucked into a stocking as part of Highland dress along with the kilt is known as a Sgian Dubh.

A dirk is also the name used for a side-arm worn by Royal Navy midshipmen and naval cadets.

The term 'dirk' is also given to a short-bladed weapon used in the Middle Bronze Age (c. 1500-1100 BC).