Borrowed from the Spanish puerta, meaning the same.
I petta. The door.
Baba i petta. Open the door.
Huchom i petta. Close the door.
Kandålo i petta. Lock the door.
Dångkulo na potta. A large door.
Did pre-Spanish Chamorros have doors? There is a difference between an entrance and a door. An entrance is simply an opening that allows access and departure. A door is a physical object that actually blocks the entrance when desired.
If our ancestors never used doors, then borrowing puerta is understandable.
But even without doors, entrances to homes, caves, lagoons and so forth certainly existed. Pale' Roman thinks sågua' served the purpose of naming any entrance. Sågua' is now almost exclusively used to refer to a channel, which is an opening or entrance in the reef allowing access in and out of shallow water as opposed to the deep sea.
Pale' Roman also makes use of the FAN+WORD+AN formula and proposed fanhaluman as an indigenous term for "door." FAN+HALOM+AN.
But hålom means "to enter" (and also "inside") so fanhaluman essentially means "entrance." But Pale' Roman uses it when translating "Gate of Heaven." Fanhaluman i Langet.
A very common trait in Chamorro is to shorten words by dropping sounds and letters at the beginning, or end or within a word. So, another form of fanhaluman is fanhakman.
From a Chamorro hymn :
I pettan i sagrårio / Påle' babaye ham
(The door of the tabernacle / Father, open for us)
Na' huyong i Saina-ta / yan nå'e ham!
(Bring out our Lord / and give Him to us!)