The /k/ sound is spelled with <c> or <k> initially, and usually <ck> or <ke> medially or finally though we also see <c> in sic and <cc> in Beccles. The /Ɵ/ sound is usually spelled with <th>.
When /Ɵ/ occurs finally in a noun, there is some instability as to whether the plural is made with /s/ or /z/. The words birth, cloth, earth, and all the ordinal numbers made with -th would usually have the /s/ inflection. The word oath would usually have a /z/ plural. Other words such as path and wreath might have either.
The contrast is between a velar stop and a dental fricative, both voiceless. It causes no problems.
The only 3-syllable pair in the list is curable/thurible. It is striking how many of the words with /Ɵ/ in the list are rather obscure ecclesiastical or literary words such as bethels or thane.
The mean density value is 1.1%. The list makes 66 semantic distinctions, a loading of 55%.
accurst athirst bark bath barked bathed barking bathing barks baths beak Beith Beccles bethels burke berth burked berthed burkes births burking berthing cane thane canes thanes catch thatch catches thatches catching thatching catcher thatcher catchers thatchers caught thought cause thaws caw thaw cawed thawed cawing thawing caws thaws clock cloth clocks cloths coal thole coals tholes come thumb comes thumbs coming thumbing corn thorn corns thorns corny thorny cornier thornier corniest thorniest court thought courts thoughts crash thrash crashed thrashed crashes thrashes crashing thrashing crawl thrall crawls thralls crew threw crone throne crones thrones crone thrown crow throe crows throes crow throw crowing throwing crows throws crumb thrum crumbs thrums crush thrush crushes thrushes crust thrust crusting thrusting crusts thrusts cud thud curable thurible curd third curds thirds cursed thirst deck death decks deaths dirk dearth dirks dearths duck doth fake faith fakes faiths forecourt forethought fork forth forks fourths frock froth frocks froths hack hath hark hearth harks hearths irk earth irked earthed irking earthing irks earths kick kith king thing kings things kink think kinking thinking kinks thinks lakh lath leaky Lethe Max maths Mick myth mix myths mock moth mocks moths murk mirth oak oath oaks oaths park path parks paths perk Perth Q's thews queues thews quack thwack quacked thwacked quacking thwacking quacks thwacks quart thwart quarts thwarts rake wraith rakes wraiths rock wrath sec saith teak teeth whelk wealth wick withe wicks withes work worth wreak wreath
John Higgins, Shaftesbury, April 2010.