As in the Triangle Shirtwaist Factory Fire.
And while we’re at it, what’s the original meaning of the term “pantywaist”? Nowadays it’s just a term for an effeminate or weak man, and even in that usage it sounds old fashioned, like something a 1930’s football coach would have used to berate his losing team.
A shirtwaist is another term for a woman’s blouse.
A shirtwaist is just a woman’s shirt that is substantially similar to a man’s shirt. (eg; collared with a button-front.)
By extension, pantywaist = “bikini briefs.” 
Also simply called “waists.” They became popular as separate-wear in the late 19th century and continued so through the 1910s, after which more modern styles became popular, and they were just called “blouses.” A “shirtwaist dress” is still the term for a dress that looks like an extended shirt, wit a belt. My grandmother still referred to blouses as “waists” till she died in '88.