From an LDS perspective, what is a key?

In the following verses (and many others), the word "key" is used in an untraditional way. Typically you would use a key to unlock a lock. The supposed "lock" is highlighted in bold in every verse. Matthew 16:19 > And I will give unto thee the keys of **the kingdom of heaven**: and > whatsoever thou shalt bind on earth shall be bound in heaven: and > whatsoever thou shalt loose on earth shall be loosed in heaven. D&C 7:7 > And I will make thee to minister for him and for thy brother James; > and unto you three I will give this power and the keys of **this > ministry** until I come. D&C 13:1 > Upon you my fellow servants, in the name of Messiah I confer the > Priesthood of Aaron, which holds the keys of **the ministering of > angels, and of the gospel of repentance, and of baptism by immersion > for the remission of sins**; and this shall never be taken again from > the earth, until the sons of Levi do offer again an offering unto the > Lord in righteousness. Is there one united meaning of the word "key" in the scriptures, from an LDS perspective?