Today a corsage is a small bouquet of flowers pinned to your bodice or worn on your wrist, but that hasn’t always been what a corsage is. Corsage used to be a term for a bodice.
While a small bouquet of flowers and a blouse may seem like very different things, the terms are actually related. Women used to gather a small nosegay of flowers to wear on their bodice, or their gentlemen admirers would send them small bouquets to be worn to an event. These nosegays were called ‘corsages’ (basically a shortening of ‘corsage bouquet’) because they were specifically meant to be worn on a woman’s corsage.
In the same way, men would wear flowers in their buttonholes, and these were (and still are, in the UK and a few other places) called ‘buttonholes’ though the name didn’t stick as well in America, and today they are more likely to call them boutonnieres (which is just French for buttonhole).
The term ‘corsage’ comes from the French cors, or body, and thus has the same root as corset. It dates back to the 15th century, but only in the 19th century did it become commonly used as a term for a bodice.
In the early 19th century a corsage was predominantly a bodice, but by the end of the century the term was used equally for both uses, so that in 1893 one might read an article describing flower clusters for a corsage and a year later an article describing the latest fashions in corsage bodices, and a few months later read:
Corsage bouquets are boldly treated to be in keeping with the puffed sleeves that rule for the nonce…A dainty corsage decoration for a young lady is composed of two light bunches of lily-of-the-valley, connected by fine sprays of amilax
The term corsage for a fitted bodice was still widely used until the start of WWII, but is rarely seen as a term for a bodice, rather than a cluster of flowers pinned to the bodice, post 1940.
A corsage usually, but not exclusively, referred to a women’s bodice, and usually, but not exclusively, referred to a tight-fitted, structured bodice.