The "OED" is the standard historical dictionary of English. If you're just checking a quick meaning, either print or database will do. More complex searching requires use of the database.
Traces the development of English from 1150 AD to the present. Entries include spelling, pronunciation, derivation, meaning, and usage. 2nd ed (1989)+ updates.
Fully searchable library of 350,000+ works of English and American poetry, drama and prose, plus biographies, bibliographies, criticism and reference sources.
Reference dictionaries and companions, including illustrations, web links, and searching individual titles or by subject area; from Oxford University Press.
Contains all titles of the Cambridge Histories series. Topics include political, economic & regional history (ancient to modern) plus language & literature, philosophy, music, religion, science, the performing arts, etc.
350+ titles in the humanities and social sciences, including the Blackwell companions and handbooks. Strengths are psychology, sociology, history, literature, philosophy, and religion.