Dependency refers to the state of relying on something or someone for support. Synonyms for this word include reliance, addiction, attachment, familiarity, and trust. When someone has a reliance on something or someone, they can also be said to be dependent on that thing or person. Some other synonyms for dependency could include the words subservience, obedience, necessity, and helplessness. In certain contexts, the word co-dependency may also be used - this term describes a situation where two people are mutually dependent on one another, with neither party being able to function without the other. All of these words convey the idea of needing something or someone in order to feel secure or stable.