For an online dictionary (Spanish, Portuguese, French, and other languages), see www.WordReference.com.
WordReference provides access to the Collins dictionaries of Spanish and French (recommended); select the checkbox "Show this tab by default" once you view something in the Collins dictionary tab to keep all searches within that resource. Users can search for inflected forms of words to bring up the main entry (i.e., viene produces the entry for the verb venir in the Spanish dictionary.) The WR Reverse dictionary tab provides a list of all the entries on "the other side" of the dictionary in which the word you are looking up appears (e.g., if you look up liberté, the reverse dictionary will show you all the entries for English words in which that French word appears).
Some users will find the layout and search functions of that resource preferable.
See also: Oxford Language Dictionaries Online for Spanish and French dictionaries.
Scholars working in the fields of literature and culture broadly, sociology, and political science often publish on historical topics, though from angles that are less typical of historians proper. Often they will examine the shifting meanings of key concepts that you might encounter in the primary sources you are working with. To historicize those concepts (that is, to situate them in the historical context in which they were used), it can be helpful to consult the work of these other scholars. If you find that a particular term or a range of related concepts is important in your primary source(s) (e.g., libertad, liberté), try searching for those terms, or English translations of them, in some of the following databases for articles and books that may be relevant:
Modern Language Association International Bibliography (MLA Bibliography)
Social Sciences Citation Index (Web of Science Core)