清澄【せいちょう】
clear, serene
澄む【すむ】
to become clear (water, air, etc.), to become transparent, to resonate clearly (e.g. voice), to become serene, to become tranquil, to be free of worries, to pronounce as an unvoiced sound
澄み切る【すみきる】
to be perfectly clear (water, air, etc.), to clear up
澄ます【すます】
to clear, to make clear, to be unruffled, to look unconcerned, to feign indifference, to look demure, to look prim, to put on airs, to strain (one's ears), to listen carefully
澄まし顔【すましがお】
composed expression, clear face