(idiomatic) To fall over (to fall from an upright or standing position to a horizontal or prone position).

(nautical) A small triangular sail having its foot extended upon the gaff and its luff upon the topmast.

(topology) subspace topology

(topology) The topology of a subset S of a topological space X which is obtained by considering any subset of S to be an open set if it corresponds to the intersection of S with some open set of X.

(topology) The topology of the real number system generated by a basis which consists of all open balls (in the real number system), which are defined in terms of the one-dimensional Euclidean metric.

(topology) The topology of the Cartesian product of two or more topological spaces which is generated from a basis whose elements are Cartesian products of open subsets of the original spaces, such that for each such Cartesian product only a finite quantity of such subsets are proper.

Alternative form of topsy-turvy

Alternative form of topsy-turvy

A mattress protector.

(nautical) A kind of gaff-topsail, used mostly by yachts having a fore-and-aft rig. It has a short "club" or "jack yard" to increase its spread.