instantaneous

Concise Oxford English Dictionary © 2008 Oxford University Press:
instantaneous /ˌɪnst(ə)nˈteɪnɪəs/

▶adjective

• 1 occurring or done instantly.

• 2 Physics existing or measured at a particular instant.

– derivatives
instantaneity noun,
instantaneously adverb,
instantaneousness noun.

– origin C17: from med. L. instantaneus, from L. instant- (from instare ‘be at hand’).