Meaning of A in English
BAD : I hope you all have a enjoyable stay.
GOOD : I hope you all have an enjoyable stay.
Always use an (NOT a ) before a word beginning with a vowel sound: 'an egg' , 'an envelope'.
BAD : The child had been a deaf since birth.
GOOD : The child had been deaf since birth.
BAD : One of the girls I share with is a British.
GOOD : One of the girls I share with is British.
Do not use a/an before an adjective (e.g. 'deaf', 'British') unless the adjective is followed by a noun: 'Her husband is disabled.'
Compare: 'The footbridge cannot be used by the disabled.' (= all people who are disabled)
BAD : My husband is doing a MSc in civil engineering.
GOOD : My husband is doing an MSc in civil engineering.
Use an (NOT a ) before an abbreviation that begins with a vowel sound: 'an MSc' 'an MP'.
See ANOTHER 6 (↑ another )
BAD : Sometimes it is difficult to live a honest life.
GOOD : Sometimes it is difficult to live an honest life.
Use an (NOT a ) before words beginning with h when the h is not pronounced: 'an honour', 'an hour'.
Longman Common Errors English vocabulary. Английский словарь распространенных ошибок Longman. 2012