in Sunday best

in (one's) Sunday best

Wearing one's very best clothes, as one would wear to a Sunday church service. Instead of some big party, let's all get dressed up in our Sunday best and go for lunch at a fancy restaurant for my birthday! This is going to be a formal event, so please come dressed in your Sunday best.
See also: best, Sunday
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

*in one's Sunday best

Rur. in one's best clothes; in the clothes one wears to church. (*Typically: be ~; get [into] ~.) All the children were dressed up in their Sunday best. I like to be in my Sunday best whenever I go out. Let's get into our Sunday best and go out for dinner.
See also: best, Sunday
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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