illation UK /ɪˈleɪʃ(ə)n/US /əˈleɪʃ(ə)n/ noun1 •The act of inferring or concluding, especially from a set of premises; a conclusion, a deduction.Now herein there seems to be a very erroneous Illation: from the Indulgence of God unto Cain, concluding an immunity unto himself […] — 1650 formsillations