The Collaborative International Dictionary of English v.0.48:

Inverse \In*verse"\, a. [L. inversus, p. p. of invertere: cf. F. inverse. See Invert.] [1913 Webster] 1. Opposite in order, relation, or effect; reversed; inverted; reciprocal; -- opposed to direct. [1913 Webster] 2. (Bot.) Inverted; having a position or mode of attachment the reverse of that which is usual. [1913 Webster] 3. (Math.) Opposite in nature and effect; -- said with reference to any two operations, which, when both are performed in succession upon any quantity, reproduce that quantity; as, multiplication is the inverse operation to division. The symbol of an inverse operation is the symbol of the direct operation with -1 as an index. Thus sin-1 x means the arc or angle whose sine is x. [1913 Webster] Inverse figures (Geom.), two figures, such that each point of either figure is inverse to a corresponding point in the order figure. Inverse points (Geom.), two points lying on a line drawn from the center of a fixed circle or sphere, and so related that the product of their distances from the center of the circle or sphere is equal to the square of the radius. Inverse ratio, or Reciprocal ratio (Math.), the ratio of the reciprocals of two quantities. Inverse proportion, or Reciprocal proportion, an equality between a direct ratio and a reciprocal ratio; thus, 4 : 2 : : 1/3 : 1/6, or 4 : 2 : : 3 : 6, inversely. [1913 Webster]The Collaborative International Dictionary of English v.0.48:

Ratio \Ra"ti*o\ (r[=a]"sh[i^]*[-o] or r[=a]"sh[-o]), n. [L., fr. reri, ratus, to reckon, believe, think, judge. See Reason.] 1. (Math.) The relation which one quantity or magnitude has to another of the same kind. It is expressed by the quotient of the division of the first by the second; thus, the ratio of 3 to 6 is expressed by 3/6 or 1/2; of a to b by a/b; or (less commonly) the second term is made the dividend; as, a:b = b/a. [1913 Webster] Note: Some writers consider ratio as the quotient itself, making ratio equivalent to a number. [1913 Webster] The term ratio is also sometimes applied to the difference of two quantities as well as to their quotient, in which case the former is called arithmetical ratio, the latter, geometrical ratio. The name ratio is sometimes given to the rule of three in arithmetic. See under Rule. [1913 Webster] 2. Hence, fixed relation of number, quantity, or degree; rate; proportion; as, the ratio of representation in Congress. [1913 Webster] Compound ratio, Duplicate ratio, Inverse ratio, etc. See under Compound, Duplicate, etc. Ratio of a geometrical progression, the constant quantity by which each term is multiplied to produce the succeeding one. [1913 Webster]