shirt-sleeve

[shurt-sleev]

adjective

not wearing a jacket; informally dressed: a shirt-sleeve mob.
warm enough to live or work in without wearing a jacket or coat: shirt-sleeve weather in November.
simple, plain, and informal; direct and straightforward in approach, manner, etc.: shirt-sleeve diplomacy.

Origin of shirt-sleeve

First recorded in 1560–70

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

He had stripped off his coat and waistcoat, and was busily at work in his shirt-sleeves.
Little Daffydowndilly
Nathaniel Hawthorne
His white locks were uncovered, and he was in his shirt-sleeves.
The Village Watch-Tower
(AKA Kate Douglas Riggs) Kate Douglas Wiggin
He was in his shirt-sleeves, his waistcoat unbuttoned and loose.
The Gentleman From Indiana
Booth Tarkington
His shirt-sleeves were rolled up, too, and his brown arms were bare to the elbows.
A Tale of Two Cities
Charles Dickens
David came in his shirt-sleeves, for he had been fetched from his work.
Heather and Snow
George MacDonald

1560s, from shirt (n.) + sleeve (n.). Usually with the notion of "without a coat."