a smart alec/aleck

smart aleck

An impudent or obnoxiously self-assertive individual, a wise guy, as in New teachers often have a hard time coping with the smart alecks in their classes. This expression, dating from the mid-1800s, probably alluded to a person of this description who was named Alec or Alexander, but his identity has been lost.
See also: aleck, smart
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

a smart alec

BRITISH or

a smart aleck

A smart alec or a smart aleck is someone who is very clever and who is often able to answer questions in a clever way. Note: People sometimes spell `alec' and `aleck' with capital initials, as names. They've got some smart alec of a lawyer from London to oppose bail. Note: You can use smart alec and smart aleck before a noun. I hate smart-aleck kids who talk like dictionaries. Note: You use this expression to show that you find someone annoying. Note: Alec or Aleck is a shortened form of the name Alexander.
See also: alec, smart
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012

smart alec (or aleck)

a person considered irritating because they know a great deal or always have a clever answer to a question.
From the male personal name Alec, a short form of Alexander.
See also: alec, smart
Farlex Partner Idioms Dictionary © Farlex 2017

a ˈsmart alec/aleck

(informal, disapproving) a person who tries to show that they are cleverer than everyone else: Some smart alec wrote in to say that the last edition of the newspaper contained 37 printing errors.
See also: alec, aleck, smart
Farlex Partner Idioms Dictionary © Farlex 2017
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