The /ɔ/ vowel is usually spelled <or>, <our>, and <oar>, but we also see <al> in call, <au> in sauce, <aw> in dawn and <ar> after <w> in war and water. The /aʊ/ diphthong is spelled <ow> or <ou>.
This is a contrast between a long vowel and a diphthong. The starting positions are fairly close in the mouth and, although there is a difference of lip-rounding, there is potential for confusion. It is a recognised difficulty for speakers of Norwegian and perhaps some others.
Interesting pairs include:
The density figure is 6.14%. The set makes 71 semantic contrasts giving a loading of 54.2%.
abort about all owl aught out awl owl awls owls bawd bowed befall befoul befalling befouling befalls befouls board bowed boar bough boars boughs bore bough bores boughs bought bout brawn brown brawny brownie call cowl called cowled calling cowling callings cowlings calls cowls cause cows caw cow cawed cowed cawing cowing caws cows chaw chow chaws chows Claud cloud daw dhow daws dhows dawn down dawned downed dawning downing dawns downs debauch debouch debauched debouched debauches debouches debauching debouching door dhow doors dhows drawers drowse drawn drown fall foul falling fouling falls fouls Fawley foully fawned found ghat gout gnaw now gorge gouge gorged gouged gorges gouges gorging gouging hall howl halls howls haul howl hauled howled hauling howling hauls howls haw how haws house hoarder howdah hoarders howdahs hoarse house horned hound horsefly housefly horseflies houseflies horseman houseman laud loud lord loud lordly loudly maw mow maws mows Morse mouse mourned mound naught knout naughts knouts nor now Norse nous pawned pound porch pouch porches pouches port pout ported pouted porting pouting ports pouts raw row roar row roars rows roared rowed roars rouse sauce souse sauced soused sauces souses saucing sousing saw sow scald scowled score scow scores scows short shout shorted shouted shorting shouting shorts shouts slaw Slough snort snout snorts snouts soar sow soars sows source souse sources souses sourced soused sourcing sousing spores spouse sport spout sported spouted sporting spouting sports spouts strawed Stroud torn town tort tout torts touts warned wound war wow wars wows waterfall waterfowl waterfalls waterfowls wrought rout yawl yowl yawls yowls
Credit: John Higgins