The term 'fade gradually' can be described by two crossword solutions: 'ERODE' (5 letters) and 'peter out' (8 letters). 'ERODE' is a verb meaning to gradually wear away or diminish, usually through the action of natural elements such as wind or water. 'Peter out' is an idiom meaning to gradually become weaker or less frequent until it stops completely. Both terms describe a gradual process of fading away.