What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1Anatomy. A tuft of small blood vessels, (in later use) specifically of arterioles in the spleen.
2Mycology and Botany. A structure resembling a paintbrush; specifically the conidium-producing body of a fungus of the genus Penicillium and related genera.
Late 16th century (in an earlier sense). From classical Latin pēnicillus pencil.