The Complete List of
English Spelling Rules

Lesson 18: -ious or -eous

In this series of lessons, you will learn useful spelling rules in English.

This lesson will give you examples of two common adjective suffixes in English: -ious and -eous so that you can learn when to use each.

two happy men

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You have learned that an adjective in English describes a noun. You can often recognize adjectives easily because of their suffixes.

Two suffixes that always form adjectives are -ious and -eous. Unfortunately there are no firm rules to tell you when to use each, but reviewing the lists below will help you learn when to use each.

1. -ious with a short U sound

a very nervous man

Poor Gerald is feeling very anxious about the presentation.

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The first thing to remember is that the adjective suffix -ious is much more common than the ending -eous. And of course, all the words ending in these two suffixes are adjectives.

There are two ways to pronounce the -ious ending. Sometimes the I is silent, so that the entire -ious ending is pronounced like "us" with a short U sound.

Here are some of the most common examples with this pronunciation:
  • ambitious
  • suspicious
  • delicious
  • religious
  • superstitious
  • conscious
  • ferocious
  • precious
  • cautious
  • vicious
  • spacious
  • prestigious
  • gracious
  • fictitious

2. -ious with a long E sound and a short U sound

a man laughing

Margaret told me a hilarious joke!

In the second way to pronounce the -ious ending, the I is not silent. It has a long E sound, followed by the short U sound, as above. So, the pronunciation of the whole -ious ending is "ee-us."

Here are some common examples of adjectives with this pronunciation:
  • previous
  • curious
  • rebellious
  • serious
  • envious
  • notorious
  • glorious
  • obvious
  • victorious
  • tedious
  • studious
  • various
  • furious
  • mysterious
  • harmonious
  • luxurious
  • oblivious

3. -eous with a short U sound

a woman in a sunflower garden

Nora's sunflowers are gorgeous!

The adjective suffix -eous is much less common than -ious. However, it can also be pronounced in the same two ways we just saw above.

Here are the most common adjectives in which the -eous ending is pronounced like "us":
  • outrageous
  • homogeneous
  • advantageous
  • courageous
  • righteous
  • nauseous
  • gaseous

4. -eous with a long E sound and a short U sound

a man and woman shaking hands

Karen was very courteous when she welcomed Ben to the office.

Just like the -ious suffix, -eous can also be pronounced with a long E sound, than a short U sound: "ee-us."

Here are the most common adjectives with this pronunciation for the -eous suffix:
  • spontaneous
  • simultaneous
  • hideous
  • miscellaneous
  • instantaneous
  • erroneous


So, let's review what we have learned about the adjective suffixes -ious and -eous in English:

  1. The suffix -ious is much more common than -eous.

  2. There are no strict rules to tell you when to use each.

  3. Both these suffixes form adjectives.
  4. Both suffixes can be pronounced as "us" or as "ee-us." It is best to learn these adjectives in groups by spelling and pronunciation.

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