At the worst

or in the highest, greatest, or most extreme degree:
the worst person.
most faulty, unsatisfactory, or objectionable:
the worst paper submitted.
most unfavorable or injurious.
in the poorest condition:
the worst house on the block.
most unpleasant, unattractive, or disagreeable:
the worst personality I’ve ever known.
most lacking in skill; least skilled:
the worst typist in the group.
that which is worst.
in the most evil, wicked, severe, or disadvantageous manner.
with the most severity, intensity, etc.; in the greatest degree.
to defeat; beat:
He worsted him easily.
at worst, if the worst happens; under the worst conditions:
He will be expelled from school, at worst.
Also, at the worst.
get the worst of something, to be defeated by; lose:
to get the worst of a fight.
if worst comes to worst, if the very worst happens:
If worst comes to worst, we still have some money in reserve.
in the worst way, Informal. in an extreme degree; very much:
She wanted a new robe for Christmas in the worst way.
Also, the worst way.
adjective
the superlative of bad1
adverb
in the most extreme or bad manner or degree
least well, suitably, or acceptably
(in combination) in or to the smallest degree or extent; least: worst-loved
noun
the worst, the least good or most inferior person, thing, or part in a group, narrative, etc
(often preceded by at) the most poor, unpleasant, or unskilled quality or condition: television is at its worst these days
the greatest amount of damage or wickedness of which a person or group is capable: the invaders came and did their worst
the weakest effort or poorest achievement that a person or group is capable of making: the applicant did his worst at the test because he did not want the job
the worst

in the least favourable interpretation or view
under the least favourable conditions

if the worst comes to the worst, if all the more desirable alternatives become impossible or if the worst possible thing happens
come off worst, get the worst of it, to enjoy the least benefit from an issue or be defeated in it
verb
(transitive) to get the advantage over; defeat or beat
adj.

Old English wyrresta, from Proto-Germanic *wers-ista- (cf. Old Saxon wirsista, Old Norse verstr, Old Frisian wersta, Old High German wirsisto), superlative of PIE *wers- “to confuse, mix up” (see worse). Phrase in the worst way (1839) is from American English sense of “most severely.”
v.

“damage, inflict loss upon,” c.1600, from worst (adj.). Related: Worsted; worsting.
see: at worst
see:

at worst
get (have) the worst of it
if worst comes to worst
in the worst way

also see under:
worse