different as night and day

(as) different as night and day

Very different. They might be identical twins, but Jim and Greg are different as night and day in personality. Patty is far more talkative than I am—we're just as different as night and day.
See also: and, different, night

*different as night and day

Cliché completely different. (*Also: as ~.) Although Bobby and Billy are twins, they are as different as night and day. Birds and bats appear to be similar, but they are different as night and day.
See also: and, different, night

different as night and day

Also, different as day and night. Totally unlike. For example, Although they are sisters, they are as different as night and day. Also see night and day.
See also: and, different, night