The term 'disappear slowly' can be described by three crossword solutions: ERODE (5 letters), FADE (4 letters), and ablate (6 letters). ERODE is a verb meaning to gradually wear away or destroy something through natural processes such as wind, water, or ice. FADE is a verb meaning to gradually become less intense, vivid, or clear. Ablate is a verb meaning to reduce in size or quantity by a gradual process. All three words describe the process of something disappearing slowly over time.