幻を追う[maboroshiwoou] to pursue an illusion
幻影[genei] phantom
幻覚[genkaku] hallucination
幻覚剤[genkakuzai] hallucinogen
幻姿[genshi] apparition

幻視[genshi] visual hallucination
幻想[gensou] illusions
幻想劇[gensougeki] non-realistic drama
幻像[genzou] phantom

愛想の良い[aisonoii] affable
意想外[isougai] unexpected
仮想[kasou] imagination
仮想記憶[kasoukioku] virtual memory
仮想空間[kasoukuukan] virtual space (e.g. in computer graphics)

回想[kaisou] reflection
回想録[kaisouroku] memoirs
楽想[gakusou] melodic subject
感想[kansou] impressions
危険思想[kikenshisou] dangerous thoughts

カバー曲[kabaakyoku] remake of another artist's song (a "cover")
サイン曲線[sainkyokusen] sinusoid
愛唱曲[aishoukyoku] favourite song
委曲[ikyoku] details
一曲[ikkyoku] tune (melody, piece of music)

迂曲[ukyoku] meander
円曲[enkyoku] roundabout way (of speaking or working)
円錐曲線[ensuikyokusen] conic curve
円舞曲[enbukyoku] waltz (composition)
演曲[enkyoku] musical program