Does English have any singularia tantum besides mass nouns?
What about a shambles? Although this used to be a plural form, today it's singular. See Oxford Dictionary Online. The first definition
- informal [treated as singular] A state of total disorder,
is never pluralized in my experience. The second definition
- [treated as singular] A butcher's slaughterhouse (archaic except in place names),
I can imagine pluralizing, but it's archaic.