beginning
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I don't think so. Antonyms will be the same part of speech. Begin or began would be antonyms for quit, and quitting would be an antonym for beginning.
courteous
probably necessary
beautiful
what is the antonym of salutation
fail, nullify, relinquish, give up, quit, abandon.
Kind is the antonym of unkind.
hard is the antonym of easy happy is the antonym of sad
Terror is an antonym for fearlessness.
The antonym of flat is round.
Letter
cease, give up, leave, quit, stop http://thesaurus.reference.com/browse/persist
cease, give up, leave, quit, stop http://thesaurus.reference.com/browse/persist