a

A, a

A a

Definitions of a word

variable noun a In music, A is the sixth note in the scale of C major. Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by Houghton Mifflin Harcourt. All rights reserved. 13
variable noun a A is the first letter of the English alphabet. Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by Houghton Mifflin Harcourt. All rights reserved. 7
variable noun a If you get an A as a mark for a piece of work or in an exam, your work is extremely good. Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by Houghton Mifflin Harcourt. All rights reserved. 4
noun a A or a is used as an abbreviation for words beginning with a, such as 'acceleration', 'ampère', or 'answer'. Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by Houghton Mifflin Harcourt. All rights reserved. 4
determiner a You use a or an when you are referring to any person or thing of a particular type and do not want to be specific. COBUILD Advanced English Dictionary . Copyright © HarperCollins Publishers 4
determiner a You use a or an in expressions such as eight hours a day to express a rate or ratio. COBUILD Advanced English Dictionary . Copyright © HarperCollins Publishers 4

noun

adjective

verb

adverb

pronoun

preposition

conjunction

determiner

exclamation

A common word. It’s meaning is known to most children of preschool age. About 100% of English native speakers know the meaning and use the word.

Most Europeans know this English word. The frequency of it’s usage is somewhere between "mom" and "screwdriver".

This diagram is provided by Google Ngram Viewer

amp — An amp is the same as an ampere.
ampere — An ampere is a unit which is used for measuring electric current. The abbreviation amp is also used.
angstrom — a unit of length equal to 10–10 metre, used principally to express the wavelengths of electromagnetic radiations. It is equivalent to 0.1 nanometre
type a — of or relating to a pattern of behavior characterized by competitiveness, a sense of urgency, impatience, perfectionism, and assertiveness, and possibly associated with an increased risk of heart disease.
vitamin a — a yellow oil, C 20 H 28 O, similar to vitamin A, obtained from fish liver.