irregular

Irregular is an adjective meaning not following a regular pattern, routine, or form. It signals departure from standard order, rhythm, or shape. The word comes from the prefix in- meaning not, combined with regular; it entered English through Latin irregularis and Old French.

In linguistics and grammar, irregular forms do not conform to standard patterns of conjugation or inflection. Examples include go — went, be — was/were, and child — children. Irregular plurals include goose — geese and man — men. Such forms arise from historical phonetic changes and language contact, and they are learned as part of vocabulary rather than by general rules.

In geometry and the sciences, irregular describes shapes, sequences, or systems lacking symmetry or equal spacing. An irregular polygon has sides or angles that are not all equal, unlike a regular polygon. Irregular galaxies or satellites orbiting a planet exhibit nonuniform structure or motion, and irregularities can occur in data, patterns, or trajectories.

In medicine, irregular denotes deviations from normal patterns, such as irregular heartbeats (arrhythmias) or irregular menstrual cycles. It may also describe atypical growth or development trajectories that do not follow a standard timetable, prompting further evaluation to determine underlying causes.

Beyond science, irregular can refer to anomalies or deviations from standard procedures or rules in everyday use, law, or auditing. The term is descriptive and non-committal, signaling that something does not fit an expected or conventional model.