Sleeves of
shirt. However, usually used to indicate a man wearing no
coat or
jacket, instead dressed in only his
shirt, or shirt and
vest. Until the mid
20th Century it was deemed
improper to be seen in your shirtsleeves in public, as a man's shirt was considered
underwear, and therefore the term had
derogatory connotations.
Nowadays it is mostly used to state a fact.
The word can also be used metaphorically, as an adjective, to signify anything that is informal.
"Shirtsleeves environment" is an environment in which no protective clothing or gear is required. Usually used in the context of astronautics. Thanks to StrawberryFrog.
"From shirtsleeves to shirtsleeves in three generations" is an adage made popular in the United States in the late 19th Century. Basically it means that it should take three generations from the time a hardworking immigrant (or otherwise struggling capitalist) amasses a fortune, to the time said immigrant's less hardworking offspring squander it and must again work for a living.