Singular—Plural Rules

Rules of changing number (Singular to Plural):

Singular	Plural
Addendum  Agendum  Aquarium  - Bacterium  Corrigendum  Cranium  - Curriculum  Datum  Dictum  Encomium  - Epithalamium  - Erratum  Exemplum  Exordium  - Flagellum  - Fulcrum  - Gymnasium  - HIlum  Hypogastrium Idolum  Medium Memorandum  Optimum  Ovum Radium  Referendum  Symposium  Ultimatum -	Addenda Agenda Aquaria Aquariums Bacteria Corrigenda Crania Craniums  Curricula Data Dicta Encomia Encomiums Epithalamia Epithalamiums Errata Excempla Exordia Exordiums Flagella Flagellums Fulcra Fulcrums Gymnasia Gymnasiums Hila Hypogastria Idola Media Memoranda Optima Ova Radia Referenda Symposia Ultimata Ultimatum

Rule: Replacing -us with -i or adding -es with -us.
Singular	Plural
Focus  Alumnus  Genius  Radius  Locus  Syllabus  Terminus  Stimulus	Foci/Focuses Alumni Genii/Geniuses Radii/Radiuses Loci Syllabi/Syllabuses Termini/Terminuses Stimuli
Rule: Replacing -is with -es:
Singular	Plural
Analysis  Axis  Basis  Crisis  Diagnosis  Hypothesis  Oasis  Thesis  Parenthesis  Synopsis	Analyses Axes Bases Crises Diagnoses Hypotheses Oases Theses Parentheses Synopses

Singular	Plural
Rule: By adding -s/x after -u.
Adieu  - Bandeau  Bureau  - Flambeau  - Milieu  Plateau -	Adidas  Adieux Bandeaux Bureaus  Bureaux Flambeaux Flambeaus Millicux Plateaux Plateaus
Rule: Replacing -ex/ix with -ices.
Appendix  - Index  Radix  Vertex -	Appendices Appendixes  Indices Radices Vertices Vertexes
Rule: Replacing -on with -a.
Criterion Phenomenon	Criteria Phenomena
Rule: Adding apostrophe 's:
Five  M.A. i	Five's M.A's i's

Exception: 

Formula — Formulae/Formulas

These nouns are always plural:

Scissors, Glasses, Trousers, Vegetables, Belongings, Goods, Cloths, Surroundings, Ashes, Cattle, Annals, Arrangements, Riches, Wages, Billiards.

These Nouns look Like Plural but they are singular:

Physics, Athletics, Arts, Gymnastics, Politics, Statistics, Optics, Ethics, Gallows, Innings, News, Mathematics, Economics.

These Nouns look Like singular but they are plural:

Gentry, Clergy, Aristocracy, Cattle, People, Vermin, Poultry, Folk, Children, Peasantry, Majority, Police.