Source : WordNet®

pessimal
     adj : of an organism's environment; least favorable for survival
           [syn: {pessimum(a)}]

Source : Free On-Line Dictionary of Computing

pessimal
     
        /pes'im-l/ (Latin-based antonym for "optimal") Maximally bad.
        "This is a pessimal situation."  Also "pessimise" To make as
        bad as possible.  These words are the obvious Latin-based
        antonyms for "optimal" and "optimise", but for some reason
        they do not appear in most English dictionaries, although
        "pessimise" is listed in the OED.
     
        [{Jargon File}]
     
        (1995-02-01)