The /ʃ/ sound is spelled with <sh>, <ti> or <ci>. The /ʒ/ sound is spelled with <si>, <su> or <zu>.
This is a contrast between two alveolar fricatives, distinguished only by voicing. Even native speakers may have a problem, but the contrast is so rare that it hardly matters.
The mean density value is very low at 0.2%. The list makes 5 semantic distinctions, a loading of 56%.
Aleutian allusion Aleutians allusions Confucian confusion Confucians confusions mesher measure meshers measures Asher azure dilution delusion dilutions delsuions
John Higgins, Shaftesbury, December 2010.