1
general::
Also, at the worst. 1. In the least favorable circumstance; under the most difficult conditions. For example, Convicted of taking a bribe, the official believed that at worst he would be sentenced to a few months in prison. [1500s] 2. In the least favorable view or supposition, as in No harm done; at the worst I'll copy the tax return again. Chaucer used this sense in Troilus and Cressida: "For at the worst, it may yet short our way." [Late 1300s] For the antonym, see AT BEST.
American Heritage Idioms
2
general::
Phrase(s): at (the) worst
in the most negative or pessimistic view. • At worst, Tom can be seen as greedy. • Ann will receive a ticket for careless driving, at the worst.
McGrawhill's American Idioms And Phrasal Verbs