quarto and sago

Reader's Digest 9月号のPuzzlesの中の問題からです。
The missing link
What do these words have in common?
FLAMING
QUART
HELL
LIMB
SAG
難しいですね。頭が固い私には分からないので直ぐに答えを見てしまいました。
All the words can have O added to their end to make another word.
Oを足された単語の内、QUARTO、SAGOは知らない単語なので憶えたい。
QUARTO:
・Macmillan Dictionary:
1. a large size of paper used in printing that measures about 26 x 20 centimeters
2. a book with pages that are quarto size
・Vocabulary.com: the size of a book whose pages are made by folding a sheet of paper twice to form four leaves
SAGO:
・Merriam-Webster's Online Dictionary: a dry granulated or powdered starch prepared from the pith of a sago palm and used in foods and as textile stiffening
・Vocabulary.com: powdery starch from certain sago palms; used in Asia as a food thickener and textile stiffener