Suffix: -ous
Source: DfE, English Appendix 1: Spelling (2013) — Years 3–4 statutory suffix
Origin: Latin -osus via Old French -ous, meaning "full of" or "having the quality of"
Purpose: Guide to the suffix -ous — forming adjectives, spelling variants (-ious, -eous), KS2 word list with definitions, and morpheme-based practice.
What it means
-ous turns a noun into an adjective meaning "full of" or "having the quality of."
danger → dangerous (full of danger)
fame → famous (having fame)
courage → courageous (having courage)
Five spelling cases
Case 1 — Add directly: danger → dangerous · poison → poisonous · mountain → mountainous
Case 2 — Drop silent e: fame → famous · nerve → nervous · adventure → adventurous
Case 3 — Drop u from -our: humour → humorous · glamour → glamorous · vigour → vigorous
Case 4 — Keep e to protect soft g: courage → courageous · outrage → outrageous
Case 5 — -ious form: ambition → ambitious · caution → cautious · suspicion → suspicious
Morpheme matrix
| -ous | -ious | (nothing) | |
|---|---|---|---|
| danger- | dangerous | — | danger |
| fame- | famous | — | fame |
| courage- | courageous | — | courage |
| humour- | humorous | — | humour |
| ambition- | — | ambitious | ambition |
| caution- | — | cautious | caution |
| mountain- | mountainous | — | mountain |
Statutory examples (Appendix 1, Y3/4)
| Base | -ous word | Case |
|---|---|---|
| danger | dangerous | Case 1 |
| poison | poisonous | Case 1 |
| mountain | mountainous | Case 1 |
| fame | famous | Case 2 |
| nerve | nervous | Case 2 |
| marvell | marvellous | Case 1 (British double l) |
| humour | humorous | Case 3 |
| glamour | glamorous | Case 3 |
| courage | courageous | Case 4 |
| ambition | ambitious | Case 5 |
| caution | cautious | Case 5 |
Dictation sentences
- The dangerous path through the mountainous terrain was famous for its difficulty.
- She was nervous but courageous, which the crowd found marvellous.
- His humorous response to the outrageous claim made everyone laugh.
- She was ambitious and cautious in equal measure — famous for both qualities.
- The glamorous event was poisonous with tension beneath the adventurous surface.
Source: DfE English Appendix 1: Spelling (2013). Etymology: Latin -osus via Old French.
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