(每日一词）theory

Theory  /ˈθɪr.i/ n. 理论;学说;意见

meaning: a formal statement of the rules on which a subject of study is based or of ideas that are suggested to explain a fact or event or, more generally, an opinion or explanation 

词根: the- 看,观察(theater)

后缀: -ory 名词后缀(factory)

e.g. He has a theory that the hole was caused by a meteorite. 他认为那个洞是陨石坠落形成的。