An alternative is defined as an option.(noun)
Corn as a side dish to an entree is an example of an alternative.
The definition of alternative is something that is a possible selection.(adjective)
The route you decided to take is an example of an alternative route.
Alternative is defined as something that does not conform to existing or mainstream standards.(adjective)
Acupuncture is an example of an alternative medical treatment.
See alternative in Webster's New World College Dictionary
Origin: ML alternativus: see alternate
See alternative in American Heritage Dictionary 4
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