Hypocatastasis is a figure of speech that declares or implies a resemblance, representation or comparison. It differs from a metaphor, because in a metaphor the two nouns are both named and given; while, in hypocatastasis, only one is named and the other is implied, or as it were, is put down underneath out of sight. Hence hypocatastasis is an implied resemblance or representation: that is an implied simile or metaphor. A hypocatastasis has more force than a metaphor or simile, and expresses as it were a superlative degree of resemblance.
Bullinger gives the following example: one may say to another, “You are like a beast.” This would be simile, tamely stating a fact. If, however, he said, “You are a beast” that would be metaphor. But, if he said simply, “Beast!” that would be hypocatastasis, for the other part of the simile or metaphor (“you”), would be implied and not stated. This figure, therefore, is calculated to arouse the mind and attract and excite the attention to the greatest extent.