Definition of fast (Entry 5 of 5) : something that fastens (such as a mooring line) or holds a fastening Synonyms & Antonyms Choose the Right Synonym More Example Sentences Learn More about fast indicating a time in advance of the correct time, as of a clock. est. In these ten days of fasting, the Lord will begin to do a mighty work in the origin of these negative words and thoughts - … Find descriptive alternatives for fast. noting or according to daylight-saving time. Synonyms for fast at Thesaurus.com with free online thesaurus, antonyms, and definitions. Fast these words for ten days: complaining, criticism, judgments, sarcasm, and gossip.