The /s/ sound is spelled with <s> or <c>. The /w/ sound is spelled with <w>.
This is a contrast between a voiceless sibilant fricative and a voiced bilabial semivowel, and can only occur initially or medially. It does not cause problems.
The only taboo word pair is sank/wamk.
Interesting pairs include:
ceiling wheeling
lapsing lapwing
saviour wavier
sorrier warrior
The mean density value is %. The list makes semantic distinctions, a loading of %.
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Credit: John Higgins