From Longman Dictionary of Contemporary Englishdeclensionde‧clen‧sion /dɪˈklenʃən/ noun [countable] 1 SLGthe set of various forms that a noun, pronoun, or adjective can have according to whether it is the subject, object etc of a sentence in a language such as Latin or German2 SLGa particular set of nouns etc that all have the same set of formsOrigin declension (1400-1500) French déclinaison, from Latin declinare “to turn aside, inflect”
