no earthly use, reason, etc.

no earthly (something)

No conceivable or practical (something). You had all day, so there's no earthly reason you couldn't have finished this on time! It's very sweet that you bought me a laptop, dear, but I'm 85—I have no earthly use for one of those things!
See also: earthly, no

no earthly ˈuse, ˈreason, etc.

(informal) used to emphasize that there is no use, reason, etc. at all: There’s no earthly reason why she shouldn’t come with us.
See also: earthly, no