difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge; "the professor's lectures were so abstruse that students tended to avoid them"; "a deep metaphysical theory"; "some recondite problem in historiography"
eellike aquatic North American salamander with small forelimbs and no hind limbs; have permanent external gills
an acoustic device producing a loud often wailing sound as a signal or warning
a warning signal that is a loud wailing sound
a sea nymph (part woman and part bird) supposed to lure sailors to destruction on the rocks where the nymphs lived; "Odysseus ordered his crew to plug their ears so they would not hear the Siren's fatal song"