:pessimal: /pes'im-l/ [Latin-based antonym for `optimal'] adj.
Maximally bad. "This is a pessimal situation." Also `pessimize'
vt. To make as bad as possible. These words are the obvious
Latin-based antonyms for `optimal' and `optimize', but for some
reason they do not appear in most English dictionaries, although
`pessimize' is listed in the OED.
-- The AI Hackers Dictionary