The term 'diminish gradually' can be described by a variety of words, all of which have five or fewer letters. TAPER, ERODE, WANE, ABATE, PARE, EBB, DWINDLE, and peters out are all synonyms for this phrase. TAPER means to become gradually narrower, ERODE means to wear away gradually, WANE means to decrease in size or intensity, ABATE means to reduce in intensity or degree, PARE means to reduce gradually, EBB means to gradually decrease in strength or intensity, DWINDLE means to become gradually smaller, and peters out means to gradually come to an end.