'Petty officer' definitions:

Definition of 'petty officer'

noun

A noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army [syn: petty officer, PO, P.O.]

From: GCIDE

Petty \Pet"ty\ (p[e^]t"t[y^]), a. [Compar. Pettier (p[e^]t"t[i^]*[~e]r); superl. Pettiest.] [OE. petit, F. petit; probably of Celtic origin, and akin to E. piece. Cf. Petit.] Little; trifling; inconsiderable; unimportant; also, inferior; subordinate; as, a petty fault; petty complaints; a petty prince. --Denham. [1913 Webster]
Like a petty god I walked about, admired of all. --Milton. [1913 Webster]
Petty averages. See under Average.
Petty cash, money expended or received in small items or amounts.
Petty officer, a subofficer in the navy, as a gunner, etc., corresponding to a noncommissionned officer in the army. [1913 Webster]
Note: For petty constable, petty jury, petty larceny, petty treason, See Petit. [1913 Webster]
Syn: Little; diminutive; inconsiderable; inferior; trifling; trivial; unimportant; frivolous. [1913 Webster]