In the coding table: CLOUD=durxs, MOON=wxxv, SKY=tbh, STAR=pcba, SUN=bwd. Code letter of 'S' is -
In the coding table: CLOUD=durxs, MOON=wxxv, SKY=tbh, STAR=pcba, SUN=bwd. Code letter of 'S' is -
S appears in SKY, STAR and SUN. Cross-referencing SUN=bwd with MOON (N=w) and CLOUD (U=d), the remaining code b consistently maps to S across all three words.
Re-check your working by substituting the answer back into the original question.