Dodo, judo, redo and undo are 4 letter words. They end with the letters do.
"Edo" is a Japanese word ending in 'do'. "Ado" is an English word ending in 'do'.
None in English.
Igloo.
Stall.
One option is the word conga.
tattoo
congo
* jumbo * giant * hefty * large
empty
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Three (3).
igloo
shampoo
utau. oo-TAH-oo
quadsquits