The term 'REFERENCE BOOK ABBR.' can be broken down into four abbreviations: DICT (4 letters), OED (3 letters), IBID (4 letters), and ETSEQ (5 letters). DICT stands for Dictionary, which is a book that contains an alphabetical list of words with their definitions. OED stands for Oxford English Dictionary, which is a comprehensive dictionary of the English language published by the Oxford University Press. IBID stands for Ibidem, which is a Latin term meaning 'in the same place' and is used to refer to a source previously cited in a work. Lastly, ETSEQ stands for Encyclopedia of the Social Sciences, which is a reference work containing articles on topics related to the social sciences.