A Momentary Lapse of Reason

a Determinative

— A is used when the following word could be any of a certain type. Compare "A book I saw on the shelf" and "The book I gave you yesterday".

a Noun

— A is the first letter of the alphabet. The letter "a" comes before "b". — In some schools, an A is a very high grade. Ron got an A on his earth science test.

momentary Adjective

— When something is momentary, it lasts for a very brief amount of time. I took a momentary glimpse at the commotion.

lapse Noun

— A lapse is an error or a failure made because of a carelessness.

lapse Verb

— If you lapse, you make one or more mistakes because of a carelessness. — If you lapse, you start to make your bad habits that you avoided before.

of Preposition

— Made using. It is a house of cards.

reason Noun

— A reason to do something is why you do it, or the cause of something. The low price was the main reason for buying it. I asked them about the reason why we should go. The police are looking for the reason for the accident. — Reason is the ability to think clearly. It's important to use reason to decide, not emotion.

reason Verb

— If you reason, you think carefully about something. — (uncommon) If you reason someone, you persuade using reasoning. I reasoned my friend into my religion.