The simultaneous presence of two mutually exclusive meanings for one word. The meaning required by the context preceding the word represses the meaning incompatible with that context.
A pun would be the active presence of both meanings simultaneously.
A good example is –
She had a night mare (which makes sense as a horrifying dream)
Unless you have other words that relate to the context of the word under contention like-
She had a night mare, black as night and skittish. She kept her night mare in a stable.
Unless it is an extended metaphor-
She had a night mare, black as night and skittish. She kept her night mare in the stable of her dreams, which plagued her sleep from which she awoke in cold sweats.