Is it ensure, insure, or assure?
late 14c., "small," from phonemic spelling of Old French petit "small" (see petit). In English, not originally disparaging (cf. petty cash, 1834; petty officer, 1570s). Meaning "of small importance" is recorded from 1520s; that of "small-minded" is from 1580s. Related: Pettily; pettiness. An old name for "Northern Lights" was petty dancers.