ninetieth

UK: /ˈnaɪntiəθ/ US: (nīn′tē ith)

WordReference Random House Unabridged Dictionary of American English © 2025

nine•ti•eth  (nīn′tē ith), adj. 

1. next after the eighty-ninth;
   being the ordinal number for 90.
2. being one of 90 equal parts.

n. 

3. a ninetieth part, esp. of one (¹⁄₉₀).
4. the ninetieth member of a series.

• Middle English nyntithe, Old English nigenteotha. See ninety, -eth² bef. 1100

Collins Concise English Dictionary © HarperCollins Publishers::

ninetieth / ˈnaɪntɪɪθ/ adjective

1. (usually prenominal) being the ordinal number of ninety in numbering or counting order, position, time, etc. Often written: 90th
2. (as noun): the ninetieth in succession

noun

1. one of 90 approximately equal parts of something
2. (as modifier): a ninetieth part
3. the fraction equal to one divided by 90 ()

WordReference Random House Learner's Dictionary of American English © 2025

nine•ty /ˈnaɪnti/   n., pl. -ties, adj. 
n. [countable]

1. a cardinal number, equal to ten times nine.
2. a symbol for this number, such as 90 or XC.
3. a set of this many persons or things.
4. nineties, [usually: the + ~] the numbers from 90 through 99, as in referring to the years of a lifetime or of a century or to degrees of temperature.

adj. [before a noun]

5. amounting to 90 in number.

nine•ti•eth, adj., n. [countable]

WordReference Random House Unabridged Dictionary of American English © 2025

nine•ty  (nīn′tē), n., pl. -ties, adj.  
n. 

1. a cardinal number, ten times nine.
2. a symbol for this number, as 90 or XC.
3. a set of this many persons or things.
4. nineties, the numbers, years, degrees, or the like, from 90 through 99, as in referring to numbered streets, indicating the years of a lifetime or of a century, or degrees of temperature:
   His grandmother is in her nineties.

adj. 

5. amounting to 90 in number.

• Middle English nineti, Old English nigontig. See nine, -ty¹ bef. 1000