late 14c., "liable to change," from Latin mutabilis "changeable," from mutare "to change," from PIE root *mei- (1) "to change, go, move" (cognates: Sanskrit methati "changes, alternates, joins, meets;" Avestan mitho "perverted, false;" Hittite mutai- "be changed into;" Latin meare "to go, pass," migrare "to move from one place to another;" Old Church Slavonic mite "alternately;" Czech mijim "to go by, pass by," Polish mijać "avoid;" Gothic maidjan "to change"); with derivatives referring to the exchange of goods and services as regulated by custom or law (compare Latin mutuus "done in exchange," munus "service performed for the community, duty, work").