My Miriam Webster Dictionary (hardcover) from 1985 lists "loose" as a synonym of lose. Stupid? Yes. Has it been corrected? I hope so. What should people use? "lose" = to misplace or cease possession of. "loose" means not tight.

Again, please people - you can not rely on spell checker for everything! Another word pair not to get confused is effect/affect. Affect is a verb - the action - and effect is a noun.