I. | ̷ ̷ ̷ ̷| ̷ ̷ adjective
: being one more than 50 in number
fifty-one years
— see number table
II. pronoun, plural in construction
: 51 countable persons or things not specified but under consideration and being enumerated
fifty-one are here
fifty-one were found
III. noun
1. : one and 50 : three times 17
2.
a. : 51 units or objects
a total of fifty-one
b. : a group or set of 51
3. : the numerable quantity symbolized by the arabic numerals 51
4. : the 51st in a set or series