transient

Concise Oxford English Dictionary © 2008 Oxford University Press:
transient /ˈtransɪənt, ˈtrɑːns-, -nz-/

▶adjective

• 1 lasting only for a short time.

• 2 staying or working in a place for a short time only.

▶noun

• 1 a transient person.

• 2 a momentary variation in current, voltage, or frequency.

– derivatives
transience noun,
transiency noun,
transiently adverb.

– origin C16: from L. transient-, transire ‘go across’.