The spelling of /k/ is <c> or <ck>. The /r/ sound is spelled <r>, <rr> or <wr> in wretch. Quite often a final <r> is silent so that a pair occurs only when the words are inflected or a derivation is made, as with barking/barring and overecall/overall. Notice how the homograph row makes pairs with Co and cow.
This is a contrast between a voiceless stop and a voiced frictionless continuant. It causes no problems.
Taboo word pairs include cock/rock, coon/rune and cunt/runt.
Interesting pairs include:
caddish radish
canker rancour
capacious rapacious
causerie rosary
cavernous ravenous
compass rumpus
coquetry rocketry
kitten written
talkie Tory
The figure for the mean density is 1.3%. The set makes 143 semantic contrasts, a loading of 54%.
altercation alteration altercations alterations baccy Barry balking boring barking barring cache rash caches rashes caddish radish cage rage caged raged cages rages caging raging cake rake caked raked cakes rakes caking raking calking coring cam ram cams rams camp ramp camped ramped camping ramping camps ramps can ran candy randy cane rain caned rained canes rains caning raining cane reign caned reigned canes reigns caning reigning cane rein caned reined canes reins caning reining canker rancour cankerous rancorous canbker ranker cankers rankers canned rand Cannes ran cant rant canted ranted canting ranting cants rants canter ranter canters ranters cap rap capped rapped capping rapping caps raps capacious rapacious capacity rapacity cape rape capes rapes capture rapture captures raptures care rare caring raring case race cased raced cases races casing racing cash rash cashes rashes cat rat cats rats catches ratches cattle rattle catty ratty cattier rattier cattiest rattiest caucus chorus caucuses choruses caught wrought cause roars causerie rosary causeries rosaries cave rave caved raved caves raves caving raving cavernous ravenous cavil ravel cavilled ravelled cavilling ravelling cavils ravels caw raw caw roar cawed roared caws roars chord roared Co roe Co row coach roach coaches roaches coal rôle coals rôles coal roll coaled rolled coaling rolling coals rolls coaming roaming coast roast coasted roasted coasting roasting coasts roasts coaster roaster coasters roasters coat rote coat wrote cob rob cobs robs cobber robber cobbers robbers cock rock cocked rocked cocking rocking cocks rocks cocker rocker cockers rockers cocky corrie cocky rocky cockier rockier cockiest rockiest cocoon raccoon cocoons raccoons cod rod cods rods code road codes roads code rode codger Roger cola roller colas rollers comb Rome comb roam combed roamed combing roaming combs roams come rum comes rums comer rummer compass rumpus con Ron cone roan cones roans Connie Ronnie coo rue cook rook cooked rooked cooking rooking cooks rooks cookery rookery cookie rookie cookies rookies cool rule cooled ruled cooling ruling cools rules cooler ruler coolers rulers coon rune coons runes coot root coots roots cope rope coped roped copes ropes coping roping coquetry rocketry cord roared core roar cored roared coring roaring cores roars corking coring cosy rosy cosier rosier cosiest rosiest cosies roses cot rot cots rots coterie rotary coteries rotaries cottar rotter cottars rotters cotton rotten cove rove coves roves cow row cowed rowed cows rows cowing rowing Cowes rouse coy Roy cub rub cubs rubs cuddle ruddle cuddled ruddled cuddles ruddles cuddling ruddling cuff rough cuffed roughed cuffing roughing cuffs roughs cuff ruff cuffs ruffs cumber rumba cumbers rumbas cunning running cunt runt cunts runts cupboard rubbered cut rut cuts ruts cutting rutting debarking debarring gawky gory gawkier gorier gawkiest goriest irking erring K ray K's rays K's raise kail rail Kaiser riser Kaisers risers Kate rate ken Rennes ken wren kens wrens kenned rend Kent rent ketch retch ketches retches ketch wretch ketches wretches key re kick rick kicks ricks kind rind kinds rinds kine Rhine king ring kings rings kink rink kinks rinks kissed wrist kites rights kitten written lackey Larry marking marring overcall overall peckish perish perking purring quay re sake sari sparking sparring stalking storing tacky tarry talkie Tory talkies Tories walking warring whirring working