This article details several dictionary services and spelling aids for Web searching. A dictionary technology was developed to be used in a variety of applications, such as orthographic verification, writing aid, natural-language processing and information storage and retrieval. The design of the technology allows building complex applications using the components developed in the earlier phases of the work in a modular fashion without extensive rewriting of computer code. Since many of the potential applications envisioned for this work have online or Web-based interfaces, the dictionaries and other computer components must have fast response and must be adaptable to open-ended database vocabularies, including chemical nomenclature. ChemSpell is an adaptation of standard spelling aid technology to large, unbounded chemical nomenclature databases. Chemical names differ substantially from normal English vocabulary, can exceed 700 characters in length, and may include embedded spaces and punctuation. Unlike traditional dictionaries that have several hundred thousand words, chemical databases may have several million chemical names. One final aspect is the ease with which the spelling aid mechanisms can be maintained. Basically, when a database is updated, keys must be generated for each chemical name and the corresponding spelling aid indexes need to be updated with the new entries. This is easily supported by databases such as Oracle, which makes it possible for ChemSpell to provide the newest entries in the database as spelling aid candidates when appropriate.