A word you add after a negative to make it stronger — to say "none at all, not even a little." It comes AFTER the noun, not before it: "no reason whatsoever," "nothing whatsoever," "none whatsoever," "no idea whatsoever." You cannot say "whatsoever no reason." It almost always sits with a negative word: no, none, nothing, not any, never. "There is no evidence whatsoever" means the evidence is zero, and the speaker is a little annoyed or very sure. Without "whatsoever" the sentence is just a fact; with it, the speaker is closing the door. It feels formal and a bit strong, so you meet it most in writing, in news, in legal papers, in complaints, and in speech when someone is being firm. In everyday talking, people more often say "at all": "no reason at all" is the relaxed version, "no reason whatsoever" the heavier one. Both are correct; "whatsoever" just presses harder. There is also an older, rarer use that is not negative, meaning "whatever, of any kind" — "any person whatsoever may enter." You will see this only in old writing, contracts, and rules. Students do not need to produce it, only to recognise it.

（用於否定句加強語氣）絲毫、任何、根本；「完全沒有」的那個「完全」。日常口語更常用 at all，whatsoever 語氣更重、更正式