pessimum vs pessimal

pessimum and pessimal both are adjectives.

Word	Noun	Adjective	Verb	Adverb
pessimum	No	Yes	No	No
pessimal	No	Yes	No	No

As adjectives, pessimum and pessimal are synonyms defined as:

pessimum and pessimal: of an organism's environment; least favorable for survival

pessimum (adjective)	pessimal (adjective)
of an organism's environment; least favorable for survival	of an organism's environment; least favorable for survival