1. A computer system for building concept knowledge from a machine-readable dictionary for use by a search engine to facilitate quick and accurate information retrieval, comprising a machine-readable dictionary including a plurality of words in a first language and a plurality of corresponding translated words in a second language, and a plurality of words in the second language and a plurality of corresponding translated words in the first language; an input device for inputting a seed word; a forward-translator for obtaining a plurality of translated words in the second language corresponding to said seed word by looking up said machine-readable dictionary; a backward-translator for obtaining a plurality of translated words in the first language corresponding to each of said plurality of translated words obtained by said translator respectively as words of the concept knowledge, by looking up said machine-readable dictionary; a synonym library for storing synonymous words of each translated word in the first language and in the second language; a frequency calculator for calculating the number of times each translated word occurs during obtaining said translated words in the second language and during obtaining said translated words in the first language; an evaluation unit for ranking said translated words in the first language and in the second language based on the synonym library and the frequency calculator; a word browser for presenting said ranked words to a user; a word selecting unit for allowing said user to select desired words among said ranked words and to delete irrelevant words among said ranked words; and means for providing said selected desired words to said search engine to perform knowledge-based information retrieval instead of keyword-based information retrieval.