Available Definitions:
1) a. - Sweet and then bitter or bitter and then sweet; esp. sweet with a bitter after taste; hence (Fig.), pleasant but painful.
2) n. - Anything which is bittersweet.
3) n. - A kind of apple so called.
4) n. - A climbing shrub, with oval coral-red berries (Solanum dulcamara); woody nightshade. The whole plant is poisonous, and has a taste at first sweetish and then bitter. The branches are the officinal dulcamara.
5) n. - An American woody climber (Celastrus scandens), whose yellow capsules open late in autumn, and disclose the red aril which covers the seeds; -- also called Roxbury waxwork.