1. 观察；观测
    Observation is the action or process of carefully watching someone or something.

    e.g. ...careful observation of the movement of the planets...
           对行星运动的仔细观测
    e.g. In hospital she'll be under observation all the time.
           医院会对她24小时密切观察。

2. 观察所得；观察资料；观测数据
    An observation is something that you have learned by seeing or watching something and thinking about it.

observation的近义词

    e.g. This book contains observations about the causes of addictions.
           该书包括有关成瘾原因的观察发现。

3. （通常指观察后发表的）评论，言论
    If a person makes an observation, they make a comment about something or someone, usually as a result of watching how they behave.

    e.g. 'You're an obstinate man,' she said. 'Is that a criticism,' I said, 'or just an observation?'.
           “你是个很执拗的人，”她说道。“你这是批评呢，”我说，“还是只是发表评论而已？”

4. 观察力
    Observation is the ability to pay a lot of attention to things and to notice more about them than most people do.

    e.g. She has good powers of observation.
           她的观察力很敏锐。