fiftieth
Concise Oxford English Dictionary © 2008 Oxford University Press:
fifty/ˈfɪfti/
▶cardinal number (pl. fifties) the number equivalent to the product of five and ten; half of one hundred; 50. (Roman numeral: l or L)
– derivatives
fiftieth ordinal number,
fiftyfold adjective & adverb.
fiftieth ordinal number,
fiftyfold adjective & adverb.
'fiftieth' also found in these Oxford entries:

