Sentence:  It is the purpose of this chapter to relate these two research traditions to each other by tracing the interaction between their two major constructs: bilingualism (on the part of psychologists) and <WSD>diglossia</WSD> (on the part of sociologists). 
Meaning of the word marked with <WSD> tags:  The coexistence in a given population of two closely related native languages or dialects, one of which is regarded as more prestigious than the other; the similar coexistence of two unrelated languages.