Given a dynamic set of k strings of total length n whose characters are drawn from an alphabet of size σ, a keyword dictionary is a data structure built on that provides lookup, prefix search, and update operations on . Under the assumption that characters fit into a single machine word of w bits, we propose a keyword dictionary that represents in either or bits of space, where is the number of nodes of a trie representing . It supports all operations in expected time on an input string of length m in the word RAM model. An evaluation of our implementation highlights the practical usefulness of the proposed data structure, especially for prefix searches — one of the most essential keyword dictionary operations.