The /ɒ/ vowel is usually spelled <o> but we also find <a> after <w> in wad. The /3/ vowel is normally spelled <er>, <ir> or <ur>, and <or> after <w> in word.
This contrast is between a short and a long vowel, one with rounded lips and one unrounded. It is not usually a problem for learners.
The only mildly taboo word pair is cock/kirk.
Interesting pairs include:
collier curlier
honest earnest
socket circuit
sophist surfaced
The density value is 5.22%. The pairs make 87 semantic contrasts, giving a loading of 54%.
accost accurst allot alert allots alerts allotted alerted allotting alerting blob blurb blobs blurbs blot blurt blots blurts blotted blurted blotting blurting bog berg bogs bergs boggle burgle boggled burgled boggles burgles boggling burgling bond burned Bonn Bern bonny Bernie bossed burst botch birch botched birched botches birches botching birching box burkes choler curler cholers curlers collar curler collars curlers chop chirp chopped chirped chopping chirping chops chirps choppy chirpy cob curb cobs curbs cock kirk cocks kirks cod curd cods curds coddling curdling col curl cols curls collie curly collier curlier cost cursed cot curt cotton curtain cottoned curtained cottoning curtaining cottons curtains dock dirk docks dirks dodge dirge dodges dirges dossed durst dot dirt dotted dirtied dotty dirty dottier dirtier dottiest dirtiest follow furlough follows furloughs god gird gods girds goggle gurgle goggled gurgled goggles gurgles goggling gurgling Goth girth Goths girths hob herb hobs herbs hobble herbal hod heard hods herds Hon Herne honest earnest honestly earnestly hot hurt hots hurts hotting hurting hots hertz jockey jerky Johnny journey lock lurk locked lurked locking lurking locks lurks mock murk mosses mercies mossy mercy moth mirth mottle myrtle mottles myrtles Nov nerve Oct irked odd erred Ollie early on earn ox irks oz errs pock perk pocked perked pocks perks pod purred poll pearl polls pearls Polly pearly pom perm poms perms posse Percy posses purses pot pert scoff scurf Scot skirt Scots skirts shock shirk shocked shirked shocking shirking shocks shirks shocker shirker shockers shirkers shot shirt shots shirts smock smirk smocking smirking smocks smirks socket circuit sockets circuits sod surd sods surds sojourn surgeon sojourns surgeons sophist surfaced splodge splurge splodges splurges spot spirt spots spurts spotted spurted spotting spurting squat squirt squats squirts squatted squirted squatting squirting toff turf toffs turfs tom term toms termz tops turps wad whirred wad word wads words wadded worded wadding wording wadi wordy want weren't was whirrs watt wert yon yearn
Credit: John Higgins