Etymology Dictionary

CALTHROP, CALTRAP,  a star-thistle, a ball with spikes for annoying cavalry.  (L. and Teut. ?)   Calthrop is gen. used to denote a ball stuck with four spikes, so arranged that one of them points upwards while the other three rest on the ground.   'Caltrappe, chaussetrappe;' Palsgrave.   'Tribulus marinus, calketrappe, sea-þistel;' Reliq. Antiq. i. 37.   M.E. kalketrappe, P. Plowman, C. xxi. 296.   A.S. calcetreppe, star-thistle, A.S. Leechdoms, iii. 316.   The most likely solution of this difficult word is to derive it from Lat. calci-, crude form of calx, the heel, and a Latinised form of the Teutonic word trap.   Scheler explains F. chaussetrappe from a barbarous Lat. calcitrapa, that which entraps the heel, which will equally well explain the A.S. calcetreppe.   Florio gives O. Ital. calcatrippa, star-thistle, where calca- is plainly supposed to be allied to calcare, to tread, the form of the Ital. word being slightly altered in order to suggest this sense.   See further under Calk and Trap.   The usual Ital. word for calthrop, viz. tribolo, is a totally different word, and plainly derived from tribulus, a calthrop, also a kind of thistle.   We cannot possibly derive the F. -trappe in chaussetrappe from L. tribulus, which is what Mahn seems to suggest.   See my note to P. Plowman, C. xxi. 296; also Catholicon Anglicum, p. 52, note 3.