Suffix: -ous
Year group: 3/4
Source: DfE, English Appendix 1: Spelling, National Curriculum for England (2013) — Years 3–4, Suffixes
Curriculum requirement: Statutory
Purpose: Years 3–4 guide to the suffix -ous — forming adjectives, spelling patterns (including -ious and -eous), and statutory word practice.
The rule
The suffix -ous is added to nouns to make adjectives meaning "full of" or "having the quality of."
danger (noun) → dangerous (adjective — full of danger)
poison (noun) → poisonous (adjective — full of poison)
mountain (noun) → mountainous (adjective — having many mountains)
When the base word ends in a silent e: usually drop the e before adding -ous
fame → famous (not fameous)
nerve → nervous
adventure → adventurous
When the base word ends in -our: drop the u before adding -ous
humour → humorous (not humourous)
glamour → glamorous
vigour → vigorous
When the base word ends in -ge: keep the e to preserve the soft g sound
courage → courageous (not couragous — the e keeps g soft)
outrage → outrageous
advantage → advantageous
Special case — -ious: when the base noun ends in -ion or when following c, t, or x, the form becomes -ious
ambition → ambitious
caution → cautious
space → spacious
(Note: the full treatment of -ious is at Y5/6. Introduce it here as a related ending.)
Etymology note
-ous came into English from Old French -ous / -eux, which in turn came from Latin -osus meaning "full of" or "abounding in." This is why -ous words tend to feel fairly formal. Many came into English after 1066 with the Norman French: dangerous, famous, marvellous, precious all have French or Latin roots.
The -our → -orous pattern reflects a difference between British and American English: British humour → humorous; American humor → humorous (same result, different route). The -our spelling is British; the -orous adjective drops the u regardless.
Examples from Y3/4 and statutory lists
(† = statutory Y3/4 word)
Straightforward (drop the -e):
- famous † (fame → fam- + -ous)
- nervous (nerve → nerv- + -ous)
- adventurous (adventure → adventur- + -ous)
Base word has no -e (add directly):
- dangerous † (danger + -ous)
- poisonous (poison + -ous)
- mountainous (mountain + -ous)
- marvellous † (marvell → note: British spelling keeps double l; US: marvelous)
Drop the -u from -our:
- humorous (humour → humor- + -ous)
- glamorous (glamour → glamor- + -ous)
- vigorous (vigour → vigor- + -ous)
Keep the -e to protect soft g:
- courageous (courage → courage+ -ous — keep e)
- outrageous (outrage → outrage-ous)
-ious form (introduce at Y3/4, deepen at Y5/6):
- ambitious (ambition → drop -ion, add -ious)
- cautious (caution → drop -ion, add -ious)
- precious (price/preci- + -ous)
Common mistakes and why they happen
| Wrong | Right | Reason |
|---|---|---|
| fameous | famous | Drop the e from fame |
| dangrous | dangerous | danger + -ous — include the e in -ous |
| humourous | humorous | Drop the u from humour before -ous |
| couragous | courageous | Keep the e — it protects the soft g |
| marvellous / marvelous | marvellous (British English) | Both are correct in their varieties; British English keeps the double l |
Word sort activity
Sort these -ous adjectives by the rule used to form them.
Adjectives: famous · dangerous · courageous · humorous · poisonous · adventurous · glamorous · outrageous · nervous · mountainous · vigorous · marvellous
| Add -ous directly | Drop the -e | Drop -u from -our | Keep -e to protect soft g |
|---|---|---|---|
Extension: Find the base noun for each adjective. What does -ous add to the meaning?
Morpheme family
The -ous ending combines powerfully with other suffixes to generate longer words:
- danger → dangerous → dangerously → dangerousness
- ambition → ambitious → ambitiously → ambitiousness
- fame → famous → famously → infamous → infamously
Show children this chain on the board. Each step adds one morpheme and changes the word class.
Dictation sentences (teacher-ready)
- It was dangerous to walk near the edge of the cliff in the wind.
- She was the most famous scientist in the country.
- The adventurers crossed the mountainous terrain for three days.
- He was nervous before the performance but felt better once he started.
- The crowd was outrageous in their celebrations after the final whistle.
- With courageous determination, she kept going even when it was hard.
Classroom questions
- What noun is hiding inside the word dangerous? What does -ous add to its meaning?
- Why does humour lose its u when we add -ous?
- Why do courageous and outrageous keep the e but famous and nervous drop it?
- Can you think of an -ous word from another subject you're studying? (Science: porous, fibrous; Geography: mountainous, cavernous)
Links to other rules
- Y5/6: -ious and -eous endings — deepening the -ious pattern introduced here
- Y2: drop the -e rule — same underlying rule applies when adding -ous
- Y3/4 rule 03: -ly suffix — many -ous adjectives form adverbs with -ly (dangerous → dangerously)
Source: DfE English Appendix 1: Spelling (2013). All statutory word examples verified against the published statutory word lists for Years 3–4.
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