_Singular_ _Plural._
Antithesis antitheses
Apex apices
Appendix appendixes _or_ appendices
Arcanum arcana
Automaton automata
Axis axes
Basis bases
Beau beaux _or_ beaus
Calx calces _or_ calxes
Cherub cherubim _or_ cherubs
Crisis crises
Criterion criteria
Datum data
Diæresis diæreses
Desideratum desiderata
Effluvium effluvia
Ellipsis ellipses
Emphasis emphases
Encomium encomia _or_ encomiums
Erratum errata
Genius genii [2]
Genus genera
Hypothesis hypotheses
Ignis fatuus, ignes fatui
Index indices _or_ indexes [3]
Lamina laminae
Magus magi
Memorandum memoranda _or_ memorandums