say it: SIK-stee-ith
sixtieth is a noun and adjective meaning "position 60 in a countable series of things". It carries 3 recorded senses.
position 60 in a countable series of things
one part in sixty equal parts
the ordinal number of sixty in counting order
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for sixtieth come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.