accidence (n.)

late 14c., in philosophy, "non-essential or incidental characteristic," also "part of grammar dealing with inflection" (mid-15c.), in some cases a misspelling of accidents, or else directly from Latin accidentia (used as a term in grammar by Quintilian), neuter plural of accidens, present participle of accidere "to happen, fall out; fall upon" (see accident). The grammar sense is because they are qualities which change in accordance with use (as gender, number, tense, case) but are not essential to the primary signification.