key
n. countablen. a small metal tool used to open a lock, like on a door or a car. It can also be a button on a keyboard or piano, or the most important thing needed to solve a problem.
n. An instrument, typically of metal, shaped to operate a lock. The term also refers to a lever on a keyboard or piano, or, by extension, a crucial element for achieving or understanding something.
I need the key to my house.
She couldn't find her car key and was late for her appointment.
Understanding the historical context is the key to interpreting the novel's complex themes and allegorical structure.
In its abstract sense, 'key' collocates with the preposition 'to' (e.g., 'the key to success').
the key of the problemthe key to the problemIn its abstract sense meaning 'a crucial element', 'key' takes the preposition 'to', not 'of'.