Lewis Short
ob-stācŭlum (noun N) : obsto
* A hinderance, obstacle (post-class.; cf. impedimentum): teneris et rarioribus parcit (fulmen), quia transitu patente minus obstaculum invenit,Sen. Q. N. 2, 52, 1: rumpere obstacula,Prud. Ham. 601; App. Flor. p. 361, 11; Arn. 2, 62; Amm. 17, 3.—In plur., of mountains, Amm. 21, 10.
Charlton T. Lewis, Charles Short, A Latin Dictionary