Now this word is distributed more evenly. The marvelous first reference is during the Unexpected Party when Bilbo thought there would be four more dwarves at the door, but no.

The Etymology notes in OED for this one are absolutely glorious:

The Indo-European base can be reconstructed with an initial labial (*p) and an internal labiovelar (*k^u).

— and many screensful of information follow which have fascinated me for almost a full cup of coffee. It is absolutely worth finding out if your local library, state library, or local community college library have an OED subscription you can use.

• 1.046 it was FIVE.
• 1.109 “Five feet high the door
• 3.040 beside the plain runes which say ‘five feet high the door
• 4.042 two, three, four, five, six,
• 6.074 Fifteen birds in five fir-trees,
• 7.009 in the battle of Five Armies.
• 7.030 mind, about five minutes between each pair of you.
• 7.063 in pairs every five minutes.
• 7.084 in five fir-trees… .’
• 7.087 He refused to wait five minutes,
• 8.108 But there were still five dwarves hanging at the end of the branch
• 11.038 A door five feet high
• 12.035 You ought to have brought five hundred burglars not one.
• 12.096 made of five hundred emeralds
• 13.055 Five hours march,
• 14.042 Only five days after the death of the dragon
• 16.004 that Dain and more than five hundred dwarves,
• 16.016 He had about five hours before him.
• 16.031 and has at least five hundred grim dwarves with him –
• 17.044 and it was called the Battle of Five Armies,

“Five, Adj. & N., Etymology.” Oxford English Dictionary, Oxford UP, September 2025, https://doi.org/10.1093/OED/1175082620.