Final answer:
In 'The Great Gatsby,' Gatsby addresses Nick Carraway with the term 'old sport' to signify their friendship and to fit in with the societal elite of the era.
Step-by-step explanation:
The term of familiarity that Gatsby uses when addressing Nick in F. Scott Fitzgerald's novel The Great Gatsby is 'old sport'. This term exemplifies the intricate nature of their relationship and also serves as an indicator of Gatsby's attempts to fit in with the aristocratic society of his time.
The phrase is used repeatedly throughout the novel by Gatsby, which builds a sense of camaraderie and illustrates Gatsby's persona as someone who clings to certain affectations to create an image of wealth and sophistication.