The Old Testament is also called ‘Ta•nach.’ In Hebrew it is not a name but the initials of the three sections of the Old Testament: Torah (Torah, the Law); ‘Ne•vi•eem’ (Prophets); and Ke•tu•vim (Writings). The Torah includes the five books of Moses (Pentateuch), and ‘De•va•rim’ (Deuteronomy) is its fifth and last book following ‘Be•re•sheet’ (Genesis); ‘Shemot’ (Exodus); ‘Va•ik•ra’ (Leviticus); and Be•mid•bar (Numbers).
Each of the Torah books is named after either the very first word in that book (as in Genesis where the very first word ‘be•re•sheet’ is the name of the book), or the second (as in Exodus where it is the second word in the verse) with one exception occurring in the book Be•mid•bar (Numbers), which gets its name from the fifth word of the fifth verse of the book.
The Book of ‘De•va•rim,’ ‘Deuteronomy,’ means: ‘words.’ It can also mean ‘things’ or ‘essences.’ Note that in the first verse of the this book, the translation of the word ‘de•va•rim’ may actually mean either one of these words.
“These are the words which Moses spoke to all Israel on this side of the Jordan in the wilderness, in the Arabah opposite the Red Sea, between Paran, and Tophel, and Laban, and Hazeroth, and Dizahab”