Entry 1 sense Webster, 1913 Deficit /dĕf'-əs-ət/ · Def·i·cit · IPA /ˈdɛfəsɪt/ 01 n. Deficiency in amount or quality; a falling short; lack; as, a deficit in taxes, revenue, etc. 1. Deficiency in amount or quality; a falling short; lack; as, a deficit in taxes, revenue, etc.