A simile (/ˈsɪməli/) is a type of figure of speech that directly compares two things.[1][2] Similes are often contrasted with metaphors, where similes necessarily compare two things using words such as "like", "as", while metaphors often create an implicit comparison (i.e. saying something "is" something else). However, there are two schools of thought regarding the relationship between similes and metaphors. The first defines them as opposites, such that a statement cannot be both a simile and a metaphor — if it uses a comparison word such as "like" then it is a simile; if not, it is a metaphor.[1][3][2][4] The second school considers metaphor to be the broader category, in which similes are a subcategory — according to which every simile is also a metaphor (but not vice-versa).[5][6][7][8] These two schools reflect differing definitions and usages of the word "metaphor" and whether or not it encompasses similes, but both agree that similes always involve a direct comparison word such as "like" or "as".
The word simile derives from the Latin word similis ("similar, like"), while metaphor derives from the Greek word metapherein ("to transfer").[3] As in the case of metaphors, the thing that is being compared is called the tenor, and the thing it is being compared to is called the vehicle.[9] Author and lexicographer Frank J. Wilstach compiled a dictionary of similes in 1916, with a second edition in 1924.