an

an is an indefinite article of a vowel-first noun

and it used to mean if

and is the first syllable in annihilate

and anhedonia

and launches both the short word ani

and the long word antidisestablishmentarianism

..

it is two-fifths

of the title of the heartbreaking stones song “angie”

..

it is nested in nana

and ends authoritarian agrarian and septuagenarian

..

is it a backward negation?

na.