mysterious

adj. misterioso, arcano, enigmático, escondido, inexplicable, oculto, sibilino

misterioso

Ex: By virtue of standing an easy first among the libraries of the region -- first in size of collection, first in financial support, and first in that mysterious quality known as 'excellence' -- Dorado was asked to assume the role.

(adj.) = misterioso
Ex: By virtue of standing an easy first among the libraries of the region -- first in size of collection, first in financial support, and first in that mysterious quality known as 'excellence' -- Dorado was asked to assume the role.