(not) at all; wholly; entirely
Dated adverb used with a negative sentence to mean 'not at all' or 'not in the least'. The positive glosses 'wholly', 'entirely' reflect the literal meaning but the word is practically always used in negative contexts.
かいくれ疑う余地はない。
There is not the slightest room for doubt.
I could not believe his story at all.