We found one dictionary that defines the word know what o'clock it is:

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1. know what o'clock it is: Wiktionary

Definitions from Wiktionary (know what o'clock it is) ▸ verb:  (dated) Synonym of know what is what ▸ Words similar to know what o'clock it is ▸ Usage examples for know what o'clock it is ▸ Idioms related to know what o'clock it is ▸ Wikipedia articles (New!) ▸ Words that often appear near know what o'clock it is ▸ Rhymes of know what o'clock it is ▸ Invented words related to know what o'clock it is