a simple valveless natural horn consisting of a long tube of brass or copper, either straight or coiled; formerly often used to announce the arrival of a mailcoach
post horn in American English
noun
a straight or coiled copper or brass horn with no valves or slide, originally used to announce mail coaches
Word origin
[1665–75]This word is first recorded in the period 1665–75. Other words that entered Englishat around the same time include: background, diffraction, newsletter, recessive, wader