名詞 obsession:

1. an irrational motive for performing trivial or repetitive actions against your will
   同義詞：compulsion
2. an unhealthy and compulsive preoccupation with something or someone
   同義詞：fixation

1. Caused or conditioned by compulsion or obsession.
   強(qiáng)迫的由強(qiáng)迫或壓制所引起或制約的
2. Her commitment to a great cause degenerated from a crusade into an obsession.
   她致力於一偉大事業(yè)，但其崇高的奮斗精神已變質(zhì)成為偏執(zhí)的狂熱。

ob.ses.sion

n.（名詞）
Compulsive preoccupation with a fixed idea or an unwanted feeling or emotion, often accompanied by symptoms of anxiety.
著魔，縈繞：不由自主地被某一定式的想法或某種不想要的感情困擾，常伴有焦慮的癥狀
A compulsive, often unreasonable idea or emotion.
妄想：一種不由自主，常常是不合理的想法或情感

【引伸】
obses.sional
adj.（形容詞）
obses.sionally
adv.（副詞）