妖怪【ようかい】
ghost, apparition, phantom, spectre, specter, demon, monster, goblin, yōkai
怪しい【あやしい】
suspicious, dubious, questionable, dodgy, shady, fishy, doubtful, unsure, uncertain, unlikely, implausible, untrustworthy, unreliable, clumsy, awkward, shaky, poor, strange, weird, eerie, spooky, uncanny, ominous (e.g. weather), threatening, dangerous (e.g. financial situation), uncertain, suspicious (of a potential amorous relation), mysterious, bewitching, alluring, enticing, enchanting
怪物【かいぶつ】
monster
怪談【かいだん】
ghost story, tale of the supernatural
怪文書【かいぶんしょ】
dubious document, anonymous document containing defamatory statements
怪人【かいじん】
mysterious person
怪しげ【あやしげ】
questionable, doubtful, suspicious
怪奇【かいき】
bizarre, strange, weird, mysterious, grotesque
奇怪【きかい】
strange, wonderful, weird, outrageous, mysterious
怪盗【かいとう】
mysterious thief, phantom thief
怪獣【かいじゅう】
monster
怪しむ【あやしむ】
to suspect
