澈 is a bound form (不能单独使用) that appears in compound words to convey the meaning of 'clear,' 'penetrating,' or 'thorough.' You most often see it in adjectives like 清澈 (qīngchè, crystal clear, of water/sky) and 透彻 (tòuchè, penetrating, of an analysis or understanding), and in literary compounds like 澄澈 (chéngchè, limpid). Because it's a bound form, you must always attach it to another morpheme — never use 澈 by itself.