fifthly

adjective

1. preceded by four others in a series; 5th
2. designating any of the five equal parts of something

Etymology: ME fifte < OE fifta < fif, five

noun

1. the one following the fourth
2. any of the five equal parts of something;
3. ☆
   1. a unit of liquid measure for alcoholic beverages, equal to a fifth of a gallon (0.757 liter)
   2. a bottle of alcohol with a capacity of one fifth of a gallon
4. Music
   1. the fifth tone of an ascending diatonic scale, or a tone four degrees above or below any given tone in such a scale; dominant
   2. the interval between two such tones, or a combination of them
5. ☆ Informal Fifth Amendment

adverb