The /ɔ/ vowel is usually spelled <or>, <our>, and <oar>, but we also see <al> in hall, <au>, <aw> and <ar> after <w> in swarm and warned. The /ʌ/ vowel is spelled <u> and unusually <ou> in touch, <o> in ton. Notice how the homograph discourse is paired with discuss in one of its two pronunciations. It also turns up with different stress contrasted with schwa in another set of lists as discourse/discus.
This is a contrast between a long and a short vowel. They are fairly close together in the mouth but do not seem to cause many problems for learners. Even for speakers of five-vowel languages, the English /ɔ/ vowel gets associated with [o] while the /ʌ/ vowel is associated with [a].
One set of taboo word pairs occurs with fork/fuck.
Interesting pairs include:
borer borough
discourse discuss
horny honey
morsel muscle
raucous ruckus
The density figure is 4.17%. The set makes 94 semantic contrasts giving a loading of 48.4%.
abort abut aborted abutted aborting abutting aborts abuts awes us balk buck balked bucked balking bucking balks bucks bauble bubble baubles bubbles bawd bud bawds buds bawdy buddy board bud boarded budded boarding budding boards buds boars buzz bores buzz borer borough borers boroughs bought but bourn bun bourns buns call cull called culled calling culling calls culls caller colour callers colours caught cut cawed cud chalk chuck chalked chucked chalking chucking chalks chucks coarse cuss corm come corms comes corning cunning Corp cup corpse cups course cuss courses cusses coursing cussing coursed cussed court cut courting cutting courts cuts daub dub daubed dubbed daubing dubbing daubs dubs dawn done dawned dunned dawning dunning dawns duns daws does discourse discuss discoursed discussed discourses discusses discoursing discussing Dorking ducking dorm dumb dormer dumber exalt exult exaltation exultation exalted exulted exalting exulting exalts exults faun fun fawn fun fawned fund fawns funds flawed flood Florrie flurry force fuss forced fussed forces fusses forcing fussing forge fudge forges fudges fork fuck forked fucked forking fucking forks fucks fours fuzz gall gull galled gulled galling gulling galls gulls Gaul gull Gauls gulls George judge Georges judges hall hull halls hulls haul hull hauled hulled hauling hulling hauls hulls haulm hum haunch hunch haunches hunches haunt hunt haunted hunted haunting hunting haunts hunts hoary hurry horny honey horsy hussy horn Hun horns Huns launch lunch launched lunched launches lunches launching lunching Maud mud Maudie muddy maul mull mauled mulled mauling mulling mauls mulls morgue mug morgues mugs morsel muscle morsels muscles morsel mussel morsels mussels mortar mutter mortared muttered mortaring muttering mortars mutters naughty nutty naughtier nuttier naughtiest nuttiest norm numb norms numbs nought nut noughts nuts ores us pawn pun pawned punned pawning punning pawns puns pork puck porker pucker porkers puckers porn pun port putt ported putted porting putting ports putts porter putter porters putters paunch punch paunches punches raucous ruckus sauce suss sauced sussed sauces susses saucing sussing scald sculled scored scud short shut shorting shutting shorts shuts shorter shutter Sean shun sorely sully sortie suttee sorties suttees spawn spun stalk stuck stored stud sword sud swords suds swarm swum talk tuck talked tucked talking tucking talks tucks talker tucker talkers tuckers thawed thud torn ton torch touch torches touches tort tut warn one warns ones wrought rut