Most compounds in English are endocentric, that is, one of the elements (typically the right-hand element) is the head of the construction. Headedness is shown most clearly by hyponymy: the compound as a whole is a hyponym of its head. For example, traffic-light is a hyponym of light, but not a hyponym of traffic.
Explanation:
Therefore bittersweet would be your endocentric compound. Because something can't be bitter while being sweet.
