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.


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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

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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

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

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

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

Review

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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