cul de something
"Cul-de-sac" is a commonly used french substantive. Moreover, it is not the only french word (or compound word for that matter) that contains "cul" and yet carries no rude or offensive meaning. Somebody already mentioned the rarer "cul-de-lampe" (an architectural artifact) and the very common "cul sec". A few more jumps to my mind :
- "Cul-de-bouteille" : the bottom of a bottle, usually wine or champagne, with a distinct shape. Figuratively very thick spectacles, Sarthe-style.
- "Cul-de-basse-fosse" : underground prison cell.
- "Cul-de-jatte": person with no lower limbs.
And our wonderful Google (pardon, Gougueule) reveals others like
- "sur cul" : maritime speak for a boat with a stern deeper in water than the bow.
- "cul-de-four" : spherical vaulted ceiling shaped roughly like an oven
- a variety of qualifiers to distinguish animal species ("cul-blanc", "cul-roux", "cul-noir"...)