What is the french word for collarbones? I don't mean the collarbones
in your body (=clavicule), but the ones that stiffen your shirt
collar.

Hello mistermiyagi

"Baleine" (whalebone) is the word you want.

Here are some "baleines" in plastic:
http://www.coudre-broder-tricoter.com/reparation/baleinecol.asp
http://www.luettges.com/fr/Commence/Baleines_de_col/hauptteil_baleines_de_col.html

And some in brass:
http://www.ctshirts.co.uk/product.aspx?DepGrpCode=&DepCode=&ProCode=BRACOL

"Baleines" explained:

"BALEINES

Elles sont utilisées pour rigidifier les pointes de col.
Vous avez le choix entre :
* Baleines amovibles : il faut les retirer au lavage.
* Baleines incorporées : on ne peut pas les retirer au lavage et sont
un petit peu plus souples.
* Cols souples sans baleine."
http://www.listerouge.fr/order_your_shirt/popup_stays.htm

You'll find more references by following this search:

baleines col OR chemise
://www.google.co.uk/search?hl=en&q=baleines+col+OR+chemise&btnG=Google+Search&meta=

I hope this helps, but please just ask if anything needs clarification.

Best wishes - Leli

Just the word I wanted. Thanks very much.