ostrogn.

Etymology: < Russian ostrog (11th cent. in Old Russian in sense ‘paling or palisade of stakes driven into the ground and sharpened at the top’ (compare Old Church Slavonic ostrogŭ in the same sense), 12th cent. in sense ‘blockhouse, fortification’) < ostryj sharp (also 11th cent. in Old Russian; compare Russian ostroga spur) < the same Indo-European base as Sanskrit aśri corner (see mediocre adj. and n.), aśani tip of a missile, ancient Greek ἄκρος tip, point (see acro- comb. form), and forms in other Indo-European languages. N.E.D. (1903) derives the word < o- around, about (compare okrug n.) + stereč′ to guard (1st person singular steregu; compare storož watchman, guard), but this etymology is now generally rejected in favour of the one given above. The connection with ostryj was, however, noted at the time of the borrowing of the word into English:1761 Philos. Trans. 1760 (Royal Soc.) 51 484 Ostrojka, a small ostrog, is a place fenced and fortified with a pallisade. made of trees..cut sharp at the top... Ostrui, in Russ, signifies sharp.