An expression of mild admiration, wonder, or surprise, and formerly of asseveration: as, O la! that is strange.n. In solmization, the syllable used for the sixth tone of the scale—that is, the submediant.n. The feminine form of the definite article in French, occurring in some names and phrases used in English.n. In chem., the symbol for lanthanum.n. A contraction of Louisiana.