OED:
<unknown>An is freq. bef. a consonant to end of 13, bef. sounded h until 18.
In standard English an is now used bef. a vowel sound (including h mute), as
an egg, an honour; a bef. a consonant (including sounded h and eu-, u-
pronounced /jU, ju:/) as a pen, a host, a eunuch, a unit. But bef. an
unaccented syll., some retain an bef. sounded h, as an historian, a smaller
number bef. eu-, u-, as an university.
geoff carver - SUNY buffalo
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