A vertical, cylindrical vessel used in chemical and petroleum processing to increase the degree of separation of liquid mixtures by distillation or extraction. Also known as column.

A tall metal structure used as a transmitting antenna, or used with another such structure to support a transmitting antenna wire.

A concrete, metal, or timber structure that is relatively high for its length and width, and used for various purposes, including the support of electric power transmission lines, radio and television antennas, and rockets and missiles prior to launching.

For a set S with a given algebraic structure, this is a set of subsets, S₀ = S, S₁, S₂, . . . , S_n, such that S_i+1 is a subset of S_i, i = 1, 2, . . . , n - 1, and each S_i is closed under all possible operations in the algebraic structure of S.