SpanishDict has a reliable online dictionary at spanishdict.com. There are also many choices of Spanish dictionaries available in printed hard copies at bookstores, both online and brick and mortar.
The SpanishDict website is a useful online dictionary that goes beyond a simple translation service such as Google Translate. SpanishDict provides the context of the definition, common conversational phrases and verb conjugations, so it allows the user to determine which Spanish word best conveys the intended message. A second option is to use a print dictionary. Merriam-Webster publishes a pocket Spanish-English dictionary, which is convenient for taking to class or along as a travel companion.