1911 Encyclopædia Britannica/Metaphor
METAPHOR (Gr. μεταφορά, transfer of sense, from μεταφέρειν, to carry over), a figure of speech, which consists in the transference to one object of an attribute or name which strictly and literally is not applicable to it, but only figuratively and by analogy. It is thus in essence an emphatic comparison, which if expressed formally is a "simile" (Lat. similis, like); thus it is a metaphorical expression to speak of a ship ploughing her way through the waves, but a simile when it takes the form of "the ship, like a plough, moves," &c. The "simple" metaphor, such as the instance given, becomes the "continued" metaphor when the analogy or similitude is worked out in a series of phrases and expressions based on the primary metaphor; it is in such "continued metaphors" that the solecism of "mixed" metaphors is likely to occur.