The following list of adjectives is special because they don’t follow the regular “-o” and “-a” endings for masculine and feminine forms, respectively; they have only one form for both genders. Check it out.

egoísta – selfish
materialista – materialistic
optimista – optimistic
pesimista – pessimistic
realista – realistic
alegre – happy
amable – kind
eficiente – efficient
elegante – elegant
excelente – excellent
grande – big
horrible – horrible
importante – important
inteligente – intelligent
interesante – interesting
pobre – poor
responsable – responsible
sociable – sociable
triste – sad
valiente – brave

Nos vemos prontito.