Know-it-all

One who knows everything; hence, a person who makes pretension to great knowledge, especially one whose didactic conversational habit conspicuously reveals his belief that he has superior knowledge on many subjects; a wiseacre; a know-all; -- usually ironical. [Colloq. & pejorative] Note: the use of this term implies that the speaker disapproves of this behavior, and may think that it is unjustified
[1913 Webster +PJC]

Also, know a thing or two; know it all; know one's way around. Be extremely knowledgeable or experienced. These idioms may be used somewhat differently, expressing overconfidence, as in Helen always knew all the answers, or thought she did, or competence, as in Bob knows a thing or two about battery technology, or ruefulness, as in I thought I knew it all about plants and then I got poison ivy, or genuine expertise, as in John knows his way around tax forms. The first term dates from the early 1900s, the second from the later 1700s, the third from the later 1800s, and the fourth, also put as know one's way about, dates from the 1500s. Also see know one's stuff; know the ropes; under tricks of the trade.

The noun has one meaning:

Meaning #1: (informal) someone who thinks he knows everything and refuses to accept advice or information from others
  Synonym: know-all

"Know-all" redirects here. For the Round the Twist episode, see Know All. For the German fairy tale, see Doctor Know-all.

See also: Knowitalls and Mr. Know-It-All

Look up know-it-all in Wiktionary, the free dictionary.

A know-it-all or know-all is either someone who has a large amount of knowledge or someone who professes to have a large amount of knowledge, but who actually knows very little at all.^[1][2]

See also

• Whiz kid
• Smart alec
• Polymath

References

1. ^ Marion Ledwig (2008). "Inconsistencies in the Christian Tradition II: The Paradoxes of Onmipotence and Omniscience". God's Rational Warriors. ontos verlag. pp. 201. ISBN 3938793872. 
2. ^ Marilyn Pincus (2004). "The Know-It-All". Managing difficult people: a survival guide for handling any employee (2nd ed.). Adams Media. pp. 75–86. ISBN 1593371861. 

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