Meaning of A in English

A

( prep. )

In process of; in the act of; into; to; -- used with verbal substantives in -ing which begin with a consonant. This is a shortened form of the preposition an (which was used before the vowel sound); as in a hunting, a building, a begging.

Webster's Revised Unabridged English Dictionary.      Пересмотренный полный словарь английского языка Webster.