ambiguous, baffling, cagey, deceitful, deceptive, difficult to catch, elusory, equivocal, evanescent, fallacious, fleeting, fraudulent, fugacious, fugitive, greasy, illusory, imponderable, incomprehensible, indefinable, insubstantial, intangible, misleading, occult, phantom, puzzling, shifty, shy, slippery, stonewalling, subtle, transient, transitory, tricky, unspecific, volatile