endocentric

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of or relating to a group of syntactically related words, at least one of which is functionally equivalent to the function of the whole group. For example, the noun table in the noun phrase the old table is endocentric because it has the same grammatical function as the whole noun phrase.
2. adj. Of or relating to a compound word whose referent is the same as the referent of one of its constituent parts. For example, the noun blackboard is endocentric in that it refers to a type of board.

Wiktionary

1. adj. grammar fulfilling the same grammatical role a one of its constituents e.g. the noun "houseboat" because "boat" is also a noun

WordNet 3.0

1. adj. fulfilling the grammatical role of one of its constituents