► related/connected adjective used about things that have a connection with each other. Connected is not used before a noun: · Physics and Maths are closely related.· The two problems are connected.· homelessness and other related issues
► linked adjective having a direct connection – often used when one thing is the cause of the other: · Skin cancer is directly linked to sun exposure and damage.· Two closely linked factors produced this result.
► interrelated/interconnected adjective used about two or more things that are connected with each other and affect each other in a complicated series of ways: · The various parts of society are closely interrelated.· The book consists of a series of interconnected essays.
► interdependent used about two or more things, countries, people etc that depend on each other, and cannot exist or continue without each other: · The two countries’ economies have become increasingly interdependent.· interdependent relationships between species· Darwin said that all life on Earth is interdependent.
► relevant adjective related to what is being discussed or to a particular area of activity: · The exam tests the way you select and organize information relevant to the question.· Applicants should have several years’ relevant experience.
► be bound up with something to be very closely connected – used about two things that need to be considered together: · The history of the city has long been bound up with the sea.· Your professional development is closely bound up with personal growth.
things that are interrelated are connected and have an effect on each other: 
Unemployment and inflation are interrelated.