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For many spellers, the three adjective suffixes -ceous / -cious / -tious can provide a world of confusion. The main reason is that all three have the same pronunciation: \shəs\. With this post, I hope the confusion can end, once and for all. These three adjective suffixes can actually be differentiated quite simply. (This rule is certainly more straightforward than the rules dictating able vs. –ible!)


This suffix, which is Latin in origin, is almost exclusively preceded by an a, so it really is spelled –aceous. (The remaining 10 or so words spelled with an -iceous can easily be looked up.) The key to this suffix is that it refers almost exclusively to physical traits. To be more specific, here are the traits you may notice when you look up words with this suffix.

  1. Adjectives describing plants, flowers, and other botanical organisms.
    • A plant that is liliaceous has characteristics of a lily or belongs to the family Liliaceae.
    • A plant that is alliaceous has characteristics of garlic or onions or belongs to the family Alliaceae.
    • A flower that is rosaceous has characteristics of a rose or belongs to the family Rosaceae.
    • A flower that is orchidaceous has characteristics of an orchid or belongs to the family Orchidaceae.
  2. Words whose definitions imply the concept of “containing.”
    • Something that is micaceous contains the mineral known as mica.
    • A butyraceous substance contains butter.
    • Something that is resinaceous contains resin.
    • A pectinaceous substance contains pectin.
  3. Words whose definitions imply or state the concept of “resembling.”
    • Something that is papyraceous resembles papyrus.
    • A sebaceous substance resembles sebum, or a fatty material secreted by the skin.
    • Something that is sericeous resembles silk.


Like the preceding suffix, the suffix –cious is also originally Latin in origin. However, unlike the preceding suffix, -cious refers to intangible qualities. Let’s look at a few of these words and see how this rule works.

  • Someone who is audacious has a lot of audacity.
  • A container that is capacious has a lot of capacity.
  • Someone who is capricious exhibits caprice.
  • An animal that is ferocious exhibits a lot of ferocity.
  • Someone who is minacious has a lot of menace.

Notice how all these words have a stem with the letter c in them. If you can link the word to a stem word you recognize with a c, and the word describes an intangible quality, then spell the word with a -cious.

You can also apply this rule to words that don’t have an obvious stem word.

  • Something that is nugacious is unimportant or inconsequential.
  • Something that is pernicious is dangerous.
  • Someone who is tenacious is stubborn and unyielding.


Consider -tious basically a twin sibling of -cious. In a nutshell, -tious, like -cious, also refers to intangible qualities. The difference is that the stem words for these adjectives tend to have the letter t in them. Here are some examples.

  • ambitious – having ambition
  • deceptious – being deceptive
  • factious – tending to form factions
  • cautious – having or marked by caution
  • superstitious – having superstition (unfounded faith in something)

Adjective Suffixes – Some Exceptions

  • licentious (from license)
  • pretentious (from pretense)
  • icteritious (from icterus and icteric; also refers to a physical trait)
  • conscientious (from conscience)
  • cementitious (refers to a physical trait)
  • excrementitious (refers to a physical trait)

Printable Word List Link: -ceous / -cious / -tious

Photo credit: Fr. Ted Bobosh