square: shaped with four sides of equal length and four right-angled corners
Every time this word appears in the Bible it describes something that has been made square: an altar, the high priest's breastpiece, a doorframe, or a temple courtyard. It is a verb, but it never shows up as an action a person performs. It only ever appears in the form that describes the finished result, so in practice it works like the adjective "square."
The word is built on the same root as the number "four," and that four-ness is the heart of it: four sides, four corners, the sides matched in length. When Exodus says the altar of burnt offering is to be "square," five cubits by five cubits, or Ezekiel measures a temple court at a hundred cubits by a hundred, this is the word doing the work.
Its home is sacred architecture. The square shape it names is not decorative but ordered and deliberate, the mark of something measured out to a precise specification. That is why it clusters in the building instructions of Exodus, the temple account of 1 Kings, and Ezekiel's visionary temple.
The New Testament's one echo of this idea is the New Jerusalem, which "lies foursquare" in Revelation 21:16, using the Greek word for square, τετράγωνος. The same ideal of a perfectly ordered, measured space carries across both testaments.