Q: I always thought the expression “thin as a rail” referred to fence rails, but I’ve read recently that it actually refers to a skinny bird called a rail. Which is correct?
A: Although quite a few birdwatchers and ornithologists believe the expression refers to avian rails (members of the family Rallidae), the rail in question is of the fence variety.
The Oxford English Dictionary has five entries for the noun “rail,” but all of its published references for “thin as a rail” or “lean as a rail” are listed under the entry for the “rail” that means a rod, stick, bar, etc. The word is derived from the Latin regula, meaning a straight stick – that is, a ruler.
The OED’s first citation for “thin as a rail” comes from Mark Twain’s Roughing It (1872): “You’ll marry a combination of calico and consumption that’s as thin as a rail.” A 1927 quotation in the dictionary, “as thin as a lath or rake or rail,” reinforces the idea that the rail involved is something man-made.
Many of the feathered rails are skinny (or, as ornithologists are wont to say “laterally compressed”), but the evidence for an avian connection to the expression is thin.
If any birders out there still have doubts, here’s a quotation from the Audubon web page for the Virginia rail (Rallus limicola):
“Although ‘thin as a rail’ refers to the rail of a fence, it aptly describes the Virginia Rail, whose narrow body allows passage through the thick vegetation found in fresh and salt water wetlands.”
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