Functional relationship between immediate constituents are defined here as denoting (1) the relationship of the parts to the whole, and (2) the relationship between parts. The first type of relationship may be defined as endocentric or exocentric [...]
- Nida (1949), Pag. 94

Endocentric constructions are those in which the unit as a whole belongs to substantially the same external distribution class as the nuclear immediate constituents or both immediate constituents (there are rarely more than two).[...] The unit 'blackbird' belongs substantially the same distribution class as 'bird', i.e. it takes the same suffix '-s' and occurs in the same positions as the noun 'bird' occur.
- Nida (1949), Pag. 94

[...] the classes are 'substantially the same' rather than 'identical', since 'blackbird' obviously does not combine with 'red' in *'redblackbird' as 'bird' does in 'redbird'.
- Nida (1949), Pag. 94