Spelling Rules -- Making Noun Plurals - Page 2


Rule 7: The plurals of words ending in -o can be formed by adding either -s or -es. Many words can be formed either way. You need to check a dictionary. Two helpful rules and a table can help.
Rule A: All words that end in a vowel plus an -o (-ao, -eo, -io, -oo, -uo) have plurals that ends in just -s.
  1. studio -studios
  2. duo --- duos
  3. trio --- trios
Rule B: All musical terms ending in -o have plurals in just -s.


  1. piano --- pianos
  2. cello --- cellos
  3. solo --- solos
-os -oes -os or -oes
  1. albinos
  2. armadillos
  3. autos
  4. bravos
  5. broncos
  6. casinos
  7. combos
  8. gazebos
  9. infernos
  1. kimonos
  2. logos
  3. maraschinos
  4. ponchos
  5. sombreros
  6. tacos
  7. torsos
  8. tobaccos
  9. typos
  1. echoes
  2. embargoes
  3. heroes
  4. potatoes
  5. tomatoes
  6. torpedoes
  7. vetoes
  1. avocados/oes
  2. buffaloes/os
  3. cargoes/os
  4. desperadoes/os
  5. dominoes/os
  6. ghettos/oes
  7. grottoes/os
  8. hoboes/os
  9. innuendoes/os
  10. lassos/oes
  1. mangoes/os
  2. mosquitoes/os
  3. mottoes/os
  4. mulattos/oes
  5. noes/os
  6. palmettos/oes
  7. peccadilloes/os
  8. tornadoes/os
  9. volcanoes/os
  10. zeros/oes
Some plural forms ending in -o end in -os or -oes. See Table above.

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