Dictionaries

• Try Dictionary.com for quick word definitions.

• One Look, pulls up definitions from more than one source, giving you a multiple list of dictionaries with definitions you can compare.

Thesauruses

• Thesaurus.com
• Wordnik

Grammar sites

• Guide to Grammar and Style, Jack Lynch
• Purdue Online Writing Lab: Grammar
• Guide to Grammar and Writing
• Common Errors in English Usage, Washington State University

Source: https://www.plainlanguage.gov/resources/reference/