Cuntline
No it has nothing to do with female anatomy — at least not obviously!
It is a nautical term for the “valley” between the strands of a rope or cable.
It may also be the space between casks stowed side by side.
According to Wikipedia’s “Glossary of Nautical Terms”: Before serving a section of laid rope eg. to protect it from chafing, it may be “wormed” by laying yarns in the cuntlines, giving that section an even cylindrical shape.
Although the word is not listed in my edition of the OED, it did make an appearance on the OUP Blog back in 2012.
The suggestion is that the word was originally cantline or contline, but from the few references I’ve found there doesn’t seem to be a lot of evidence for this. And of course it is always possible that, to the male nautical mind, anything with a “crack” or “crease” is going to be associated with the female pudenda.