The /z/ sound is spelled with <z>, <s> or <se>. The /r/ sound is spelled with <r> or <rr>. 10 pairs are accounted for by plurals of compound nouns which have an internal linking -r, such as hanger-on.
This is a contrast between a sibilant fricative and a retroflex continuant, both in the alveolar region of the mouth and both voiced. It can only occur initially or medially. It is not a problem, although the /r/ sound may be troublesome for some learners.
The mean density value is low at 0.3%. The list makes 40 semantic distinctions, a loading of 68%.
apposition apparition brothers-in-law brother-in-law buzzer borough buzzers boroughs causing coring chuckers-out chucker-out daughters-in-law daughter-in-law fathers-in-law father-in-law fezzes ferries fuzzier furrier gauzy gory gauzier gorier gauziest goriest hangers-on hanger-on hussar hurrah hussars hurrahs lookers-on looker-on mothers-in-law mother-in-law pausing poring pausing pouring runners-up runner-up scissors sirrahs sisters-in-law sister-in-law tawses Tories whippers-in whipper-in Z read Z red Z's reds zany rainy zanier rainier zaniest rainiest zap rap zapped rapped zapping rapping zaps raps zee re Zen Rennes Zen wren zest rest zest wrest zestful restful zestfully restfully zinc rink zing ring zip rip zipped ripped zipping ripping zips rips zone roan zones roans zone Rhone zoo roo zoo rue zoos rues zoom rheum zoomed roomed zooming rooming zooms rooms zoos ruse
John Higgins, Shaftesbury, November 2010.