The /z/ sound is spelled with <s>, <ss>, <c> or <sc>. The /ʃ/ sound is spelled with <sh>.
This is a contrast between a voiced sibilant fricative and a voiceless fricative, fairly close together in the mouth. The only difference apart from voicing is the way the air is released, through a groove made by the tongue for /z/ and at the front of the tongue for /ʃ/. It can be a problem for Scandinavian, German and Spanish learners.
Several of these pairs arise from contrasting a plural noun with an adjective derived from the same root, such as softies/softish or bookies/bookish. Other interesting pairs include:
The mean density value is very low at 0.5%. The list makes 46 semantic distinctions, a loading of 69%.
as ash boars borsch bookies bookish brandies brandish brownies brownish caddies caddish cherries cherish craze crèche crazes crèches dizzy dishy dizzier dishier dizziest dishiest dizzies dishes do's douche fairies fairish fizz fish fizzes fishes fizzing fishing fizzed fished fizzy fishy fizzier fishier fizziest fishiest flurries flourish goes gauche goodies goodish has hash keys quiche leas leash liveries liverish Mars marsh mizzen mission mizzens missions monkeys monkish muzzy mushy muzzier mushier muzziest mushiest navies knavish parries parish piggies piggish polys polish readies reddish slaveys slavish softies softish sweeties sweetish swiz swish tsar shah tsars shahs turkeys Turkish was wash wells Welsh whiz wish whizzes wishes whizzing wishing Z shed Z's sheds zee she zees she's zip ship zipped shipped zipping shipping zips ships zipper shipper zippers shippers Zoe showy zone shown zoo shoe zoos shoes
John Higgins, Shaftesbury, November 2010.