permanganic acid: an unstable purple acid (HMnO4) known only in solution or of permanganate salts
acid: any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt
fret: a small bar of metal across the fingerboard of a musical instrument; when the string is stopped by a finger at the metal bar it will produce a note of the desired pitch