[ 'kaltrəp ]
(also caltrap )
■ noun
1》 a spiked metal ball thrown on the ground to impede wheeled vehicles or (formerly) cavalry horses.
2》 a creeping plant with woody carpels that typically have hard spines. [Genus Tribulus .]
3》 (also water ~ ) another term for water chestnut (in sense 2).
Origin
OE calcatrippe , from med. L. calcatrippa , from calx 'heel' or calcare 'to tread' + a word related to trap 1 .