1
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Phrase(s): *off base
1. Lit. [of a runner in baseball] not having a foot touching the base. (*Typically: be ~; get ~.) • The runner was off base but the first baseman didn’t tag him out. 2. Fig. unrealistic; inexact; wrong. *Typically: be ~; get ~.) • I’m afraid you’re off base when you state that this problem will take care of itself. • You’re way off base if you think I was to blame!
McGrawhill's American Idioms And Phrasal Verbs
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Wrong, relying on a mistaken premise, as in His description of the accounting system was totally off base. This metaphoric term originated in baseball, where a runner who steps off a base can be put out. [c. 1940]
American Heritage Idioms