incomprehensible
inexplicable
Greek to one
ambiguous
arcane
beyond understanding
cabalistic
impenetrable
inarticulate
incognizable
incoherent
ineffable
mystic
numinous
obscure
past comprehension
rambling
unaccountable
unconnected
unfathomable
unguessed
unintelligible
unknowable
unsearchable
baffle
emotionless
enigmatic
immovable
impassive
implacable
indifferent
irresistible
mysterious
placid
sinister
sombre
thoughtful
unreadable
unruffled
disputable
immutable
indisputable
irrefutable
mutable
suitable
unsuitable