ninetieth
Concise Oxford English Dictionary © 2008 Oxford University Press:
ninety/ˈnʌɪnti/
▶cardinal number (pl. nineties) equivalent to the product of nine and ten; ten less than one hundred; 90. (Roman numeral: xc or XC)
– derivatives
ninetieth ordinal number,
ninetyfold adjective & adverb.
ninetieth ordinal number,
ninetyfold adjective & adverb.
'ninetieth' also found in these Oxford entries:

