The definition of common is something that belongs to or is shared by two or more people or the community at large.(adjective)
An example of common is the knowledge of drivers to stop at a red light.
See common in Webster's New World College Dictionary
Origin: ME commun < OFr comun < L communis (OL comoinis), shared by all or many < IE *kom-moini-, common (< *kom, com- + *moini-, achievement < base *mei-, to exchange, barter) > OE gemæne, public, general, Ger gemein: see mean
See common in American Heritage Dictionary 4
adjective com·mon·er, com·mon·est
Origin: Middle English commune
Origin: , from Old French commun
Origin: , from Latin commūnis; see mei-1 in Indo-European roots.
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