The Keyhole Neckline

Keyhole necklines are very simple to explain: they are necklines close along the neck and shoulders with an opening starting at the neck and opening outward to expose a bit of either collarbone or back (or both).  They keyhole gets its name because it originated as a small round shaped slit, resembling very much the keyhole openings on doorknobs.
Nowadays keyholes can vary in shape from slits, tear drops, circles, diagonals, or anywhere in between.  No matter the shape all keyholes always close together at the top of the neckline, front or back and are held by a fastener or sewed closed.

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This Birnbaum & Bullock gown is the best example of the true and typical keyhole: a barely there slit with a tiny button for the closure.  This gown also illustrates the lovely retro detail keyhole necklines can have.

Credits: Birnbaum & Bullock, couture collection, style "Sonia".

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Here is a lace trimmed keyhole back from Blue by Enzoani.  Admittedly it appears not to be too dramatic or decorative a keyhole; it actually looks more like a slit that's left from the top button of the back lace panel.  Still, I like the little peek of polka dots on the sheer panel.

Credits: Blue by Enzoani, 2013 collection, style "Fada".

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This Amanda Wakeley gown features a keyhole that is lower on the bodice, but still fastens at the top of the strapless neckline.  It is a good example of a diagonal shaped keyhole.

Credits: Amanda Wakeley, Africa Look Book, style no. AW175.

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Here is a lovely and decorative lace and embellishment trimmed keyhole from Claire Pettibone.  In this example the back neckline dips to a small v before opening to a round keyhole.

Credits: Claire Pettibone, Spring 2013, style "Beauty".

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This striking Sherri Hill is another great example of a diagonal shaped keyhole.  It sits higher on the bodice but exposes a bit more than all the other keyholes pictured.

Credits: Sherri Hill, Fall 2012, style no. 2960.