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Prepositional phrase

of an, or of a before vowels

1. (somewhat dated) Belonging to the same.

   The two main players were roughly of an age.

2. (regional) Indicates a more or less habitual activity during the given part of the day.

   Of an evening, I like to play chess. i.e., On some evenings, I like to play chess.

   Of a morning, they would work in their garden. i.e., They generally worked in their garden in the morning.

Usage Note

The first sense functions as an adjective and is generally used with be. The second sense functions as an adverb.

The phrase of a can also occur naturally in a prepositional phrase using of (e.g., the shell of an egg).