The spelling of /t/ is usually <t> or <tt>, but we also often see <ght>, <th> in Thai, and a silent-letter combination <bt> in debt. The /f/ sound is usually <f>, <ff>, or <ph> in sphere and phone. The homograph tear makes pairs with fair and fear, and I have shown the partial homograph staffs/Staffs in pairs with starts and (when capitalised) stats.
The contrast is between a plosive and a fricative, both voiceless but well separated in the mouth. It is not a problem for learners.
Pairs involving taboo words are tart/fart and tuck/fuck.
Interesting pairs include:
The mean density value is 2.5%. The list makes 239 semantic distinctions, a loading of 51%.
ate F attend offend attended offended attending offending attends offends attics affix attire afire battle baffle battled baffled battles baffles battling baffling beat beef beating beefing beats beefs bit biff bits biffs but buff butt buff butting buffing butts buffs butter buffer butters buffers cart calf cat caff cats caffs cert serf certs serfs chart chaff charting chaffing charts chaffs cheat chief cheats chiefs contest confessed contuse confuse contused confused contuses confuses contusing confusing contusion confusion cot cough cots coughs cottar coffer cottars coffers cut cuff cuts cuffs cutting cuffing dealt delf debt deaf debtor deafer detect defect detected defected detecting defecting detects defects detection defection detective defective detector defector detectors defectors deter defer deterred deferred deterring deferring deters defers detract diffract detracted diffracted detracting diffracting detracts diffracts detraction diffraction detractions diffractions dot doff dots doffs dotting doffing feat feoff feats feoffs feet feoff fight fife fights fifes GATT gaff Graz graphs greet grief greets griefs hart half heart half heighten hyphen heightened hyphened heightening hyphening heightens hyphens hoot hoof hoots hoofs humped humph hut huff huts huffs inter infer interred inferred interring inferring inters infers interior inferior interiors inferiors internal infernal internally infernally it if jet Geoff knight knife knighting knifing knights knifes lied leaf light life lighter lifer lighters lifers looter loofah looters loofahs magnetize magnifies mutt muff mutts muffs natty NAAFI night knife nights knifes nit niff nits niffs oat oaf oats oafs otter offer otters offers paltry palfrey pelt pelf protest professed putt puff putts puffs putting puffing putty puffy quit quiff quits quiffs quoit coif quoits coifs rattle raffle rattled raffled rattles raffles rebut rebuff rebuts rebuffs rebutting rebuffing ret ref retract refract retracted refracted retracting refracting retracts refracts retraction refraction retractions refractions right rife rite rife root roof rooting roofing roots roofs rootless roofless route roof routes roofs rut rough ruts roughs rutting roughing sate safe sates safes satire sapphire satires sapphires Scot scoff Scots scoffs scut scuff scuts scuffs scuttle scuffle scuttled scuffled scuttles scuffles scuttling scuffling sheet sheaf sheltered Shelford shuttle shuffle shuttled shuffled shuttles shuffles shuttling shuffling silt sylph silts sylphs skirt scurf skit skiff skits skiffs skittle skiffle slut slough sluts sloughs start staff starting staffing starts staffs stats Staffs steer sphere steers spheres stinks sphinx T fee T's fees ta fa ta far tab fab table fable tabled fabled tables fables tacit facet tacked fact tact fact tactual factual tag fag tagged fagged tagging fagging tags fags tail fail tailed failed tailing failing tails fails taint faint tainted fainted tainting fainting taints faints taint feint tainted feinted tainting feinting taints feints take fake takes fakes taking faking tale fail tales fails talk fork talked forked talking forking talks forks tall fall taller faller tallow fallow tame fame tamed famed tan fan tans fans tanned fanned tar fa tar far tare fair tares fairs tare fare tares fares tart fart tarted farted tarting farting tarts farts taste faced tat fat tats fats tatted fatted tatting fatting tatter fatter tatty fatty tattier fattier tattiest fattiest taught fort taught fought taut fort taut fought tawse fours tea fee teas fees teacher feature teachers features tear fair tears fairs tear fare tears fares tearing faring tear fear tears fears tearful fearful tearfully fearfully tearless fearless teat feet Ted Fed tee fee tees fees teeing feeing teed feed tell fell telling felling tells fells ten fen tens fens tend fend tended fended tending fending tends fends tender fender tenders fenders tense fence tensed fenced tenses fences tensing fencing tenser fencer term firm termed firmed terming firming terms firms tern fern terns ferns terrace ferrous Terry ferry tether feather tethered feathered tethering feathering tethers feathers Thai fie Thame fame tickle fickle ticks fix tiddler fiddler tiddlers fiddlers tie fie tight fight tights fights tighter fighter tilde filled tile file tiled filed tiles files tiling filing till fill tilling filling tills fills tilled filled tilth filth tin Finn tin fin tins fins tine fine tines fines tined fined tined find tire fire tired fired tires fires tiring firing tit tiff tits tiffs tizzy fizzy toe foe toes foes tog fog togged fogged togging fogging togs fogs toil foil toiled foiled toiling foiling toils foils told foaled toll foal tolling foaling tolls foals tolled foaled tolled fold tome foam tomes foams ton fun tone phone toned phoned tones phones toning phoning tonic phonic tonics phonics Tony phoney tool fool tooled fooled tooling fooling tools fools tootle footle tootled footled tootles footles tootling footling top fop tops fops toque folk toques folks tor for tor fore tor four tors fours tore for tore fore tore four torn faun torrid forehead tot toff tots toffs tourney ferny tow foe tows foes toy Fowey traction fraction trade frayed trail frail trailer frailer trait freight traits freights traitor freighter traitors freighters trance France tray fray trays frays tread Fred tree free treed freed treeing freeing trees frees trees frieze trench French trend friend trends friends trier friar triers friars trill frill trilled frilled trills frills trite fright trot trough trots troughs trump frump trumps frumps try fry tried fried trying frying tries fries tuck fuck tucked fucked tucking fucking tucks fucks tucker fucker tuckers fuckers tug fug tugs fugs tumble fumble tumbled fumbled tumbles fumbles tumbling fumbling tumbler fumbler tumblers fumblers tun fun tunnel funnel tunnelled funnelled tunnelling funnelling tunnels funnels tunny funny turn fern turns ferns tut tough tuts toughs Tyne fine wait waif waits waifs waiter wafer waiters wafers wart wharf warts wharfs wattle waffle wattles waffles whit whiff white wife Wight wife wilt Wilf wit whiff wits whiffs writ riff writs riffs write rife Writtle riffle
John Higgins, Shaftesbury, January 2010.