A paving stone that forms part of a kerb / curb(noun)
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Use "kerbstone" in a sentence
"The zappee only has to fall badly and hit his head on a kerbstone and he could be dead."
"The practise of harmonising popular tunes by ear became popular throughout the 1920s in places where men met up regularly – in barbershops, for instance, although the style was also referred to as "kerbstone harmony"."
"We suspect that she had a brief faint when at the wheel last week, when she bumped against a kerbstone."