The Old Testament is a collection of religious texts that form part of the Christian and Jewish faiths. The term 'Old Testament Book' refers to any of the books contained within this collection. The crossword solutions for this term are DEUT (4 letters), EZR (3 letters), HAB (3 letters), ISA (3 letters), NEH (3 letters), and ESTH (4 letters). These abbreviations refer to the books of Deuteronomy, Ezra, Habakkuk, Isaiah, Nehemiah, and Esther, respectively.