1
general::
Phrase(s): *sick as a dog
Cliché very sick; sick and vomiting. (*Also: as ~.) • We’ve never been so ill. The whole family was sick as dogs. • Sally was as sick as a dog and couldn’t go to the party.
McGrawhill's American Idioms And Phrasal Verbs
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general::
Very ill, especially from a stomach malady. For example, I don't know what was in that stew but I was sick as a dog all night. This simile was first recorded in 1705. Why a dog should be viewed as particularly sick remains unclear.
American Heritage Idioms