nag [ME] In the sense ‘to find fault persistently’, nag was originally a northern English expression meaning ‘to gnaw or nibble’ that probably came from Scandinavia or Germany. The first written evidence is from the early 18th century, but the word may well be earlier, as dialect expressions are often used for a long time before they appear in print. Nag meaning ‘an old or worn-out horse’ is a different word. It is Middle English and may be from early Dutch, or it could be related to neigh [OE]. See also hack, jade.