βασιλεία (basileia)

The Greek word βασιλεία (basileia) means, according to the lexicon, “royal power, kingship, dominion, rule - not to be confused with an actual kingdom but rather the right or authority to rule over a kingdom.”

Thus, depending upon the context, the term could be translated variously:

When the context regards kingship or authority - as  used sometimes in Jesus' teachings, the reference is to the authority of God. It can thus be translated to God's "authority" or "power" in these cases. However, in other contexts, Jesus used the word in a different manner.

For example, we find this statement made by Jesus:
“For indeed, the kingdom of God is within you.” (Luke 17:21, NKJV)
This and other statements by Jesus contradict the notion of βασιλεία (basileia) being translated to a physical place, as "kingdom" would infer.

Rather, Jesus is using the word to describe becoming dedicated and dependent upon God's authority - thus taking sanctuary in Him: Taking refuge in God. Thus a better translation of this verse would be:
“For indeed, the sanctuary of God is within you.” (Luke 17:21)
This is consistent with the ancient use of this word as well. In ancient times, tribes and nations fought each other vigorously for territory. Those kings who were strongest provided protection - refuge – or sanctuary – to their citizens.

With this in mind, for those instances where βασιλεία (basileia) is being described as a place - a place of refuge or sanctuary – the word sanctuary may also be appropriate. A place of sanctuary is often sought for those without protection. This can be appropriately used for Jesus' teachings when the context is the spiritual realm - a place of protection that can be entered into following the death of the physical body.

Furthermore, everywhere and everything is part of God's kingdom. To stipulate anything else would be to contradict God's omnipotence. Therefore, a translation of βασιλεία (basileia) to "kingdom" would be inappropriate in the context of Jesus' teachings. If one accepts the Supreme Being as the Creator and Owner of everything - then there is not any place or thing that is not part of His kingdom.

Rather, God also provides those who seek Him special mercy: He provides sanctuary to those who seek refuge in Him. In this way, one may enter into God's sanctuary, but also God's sanctuary can be within because seeking His refuge comes from the heart.

Thus “sanctuary” is an appropriate translation of βασιλεία (basileia) when the context is one who accepts and comes within the governance and authority of the Supreme Being. This concept is consistent with David's teachings:
If you say, "The LORD is my refuge," and you make the Most High your dwelling, no harm will overtake you, no disaster will come near your tent. (Psalm 91:9-12 NIV)
When used in conjunction with the Greek word οὐρανός (ouranos) - which refers to "the heavens" - the spiritual realm - this would provide the context for taking refuge or sanctuary within the spiritual realm - and one who accepts that authority of God present there is thus taking sanctuary or refuge in the Supreme Being.

When used in conjunction with the Greek word υἱός (huios) - this would refer to a person who is a follower of God's authority - meaning someone who has taken refuge or sanctuary in the Supreme Being.