Definition of on the horn
- When I finally got him on the horn he said he couldn't come.
: one of the usually paired bony processes that arise from the head of many ungulates and that are found in some extinct mammals and reptiles: such as
: one of the permanent paired hollow sheaths of keratin usually present in both sexes of cattle and their relatives that function chiefly for defense and arise from a bony core anchored to the skull — see cow illustration
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