Word Origin and History for first marquis of lansdowne
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.