conceit

1. An extended metaphor. Popular during the Renaissance and typical of John Donne or John Milton. Unlike allegory, which tends to have one-to-one correspondences, a conceit typically takes one subject and explores the metaphoric possibilities in the qualities associated with that subject. (Silva Rhetoricae)

2. 1st. Conceit.
This word formerly meant "concept," that is, a "conception," and implied a sentiment, a striking thought. (De Mille)

2. At present it is used to signify sentiments that are strained or far-fetched, especially when presented in the form of figures. (De Mille)

1. Robert Herrick's "The Vine". (Silva Rhetoricae)

2. Thus Pope:
"Some to conceit alone their works confine,
And glittering thoughts struck out at every line." (De Mille)