Compounds often have a characteristic stress pattern (accent pattern). The main stress (position of heaviest accent) comes on the leftmost member of the compound. Certainly the majority of what are usually considered compound words exhibit this feature.
The compound movie star is pronounced MOVIEstar (where capital letters indicate the location of the heaviest accent), not movieSTAR; the compound bathroom is pronounced BATHroom, not bathROOM. The American President's residence is the WHITEhouse, which is a compound, as opposed to WHITE HOUSE.
The stress pattern can sometimes be a clue to whether a sequence of two words is a compound noun or not. For example, the sequence high and chair can be pronounced either HIGHchair, in which case it is a compound noun denoting a special kind of chair that babies sit in; or it can be pronounced highCHAIR, in which case it is simply the noun chair modified by the adjective high, denoting some chair that happens to be high.
Unfortunately, the stress criterion is not found in all compounds. There are compounds like APPLE PIE, MANMADE and EASY-GOING which show no accent reduction.
A purely phonologically based division would make BLACKberry a compound but black PUDDING free sequence, BLACKlist a compound but black MARKET a free sequence. Equally striking is the fact that whereas Oxford ROAD (also Oxford AVENUE, etc.) would be a free collocation, OXFORD Street would be a compound. These inconsistencies underline the fact that the category of compounds is a grammatical one, and that, although there is a tendency for it to be phonetically marked in a certain way, such marking is not perfectly regular.