n.1 placing side by side; juxtaposition.
2 Gram. the placing of a word next to another, esp. the addition of one noun to another, in order to qualify or explain the first (e.g. William the Conqueror; my friend Sue).
Derivatives:
appositional adj.
Etymology: ME f. F apposition or f. LL appositio (as APPOSITE, -ITION)