Analysis -- Analyses
Thesis -- Theses
Crisis -- Crises
Basis -- Bases
Parenthesis -- Parentheses
Curriculum -- Curricula
Memorandum -- Memoranda
Datum -- Data
Bacterium -- Bacteria
Medium -- Media
Criterion -- Criteria
Phenomenon -- Phenomena
Stimulus -- Stimuli
Radius -- Radii
Syllabus -- Syllabi