“However, over the next several months his health began to worsen again.”
“This account was immediately preceded by Plutarch's description of Olympias'difficult character and its tendency to worsen tensions between father and son.”
“Many autistics avoid gluten, because they think it may worsen their symptoms.”
worst
(archaic, transitive) To make worse.
(dated, intransitive) To grow worse; to deteriorate.
“That might be the only positive Woods was able to glean from his week of worsts.”
“It's hard to remember if this has been declared before, there have been so many worsts, lowest and darkest mentioned in previous months.”
“The Mets' bullpen, which entered with a 5.59 earned run average and 13 blown saves, both major-league worsts, got plenty of work, but without duress.”
worstest
(archaic) second-person singular simple present form of worst