Aside from 'mo':
macaco
machismo
macho
macro
madrono
maduro
maestoso
maestro
mafioso
magneto
magnifico
majordomo
makimono
mako
mambo
mango
manifesto
manito
mano
maraschino
marcato
marengo
marrano
martello
matzo
mayo
medico
memento
memo
mendigo
meno
menudo
mercapto
merino
mesteso
mestino
mestizo
metro
mezzo
mho
micro
micromho
mikado
milesimo
millimho
milo
mimeo
misdo
miso
moderato
modulo
mojo
molto
momento
mondo
mongo
mono
montero
moo
morello
morpho
morro
mosquito
mosso
motto
moustachio
mozo
muchacho
mucho
mucro
mulatto
mundungo
mungo
muscovado
mustachio
Five letter words that start and end with letter O are outdo and outgo.
An Italian company name that begins with "R" and ends with "o" is Roncato.
Yes. The island name Borneo ends with an "oh" sound, and open begins with an "oh" sound. This is a long O.
overdo
Actually, it starts and ends with "M", but you remove the first "M" and insert an "O" ANYWHERE in the word, not just replace "M" with "O"
oneodeoreoboeoscillateorangeogreoperateopineobliteratedobdurateobsolete
Quizno
the naswer is .............................
OSLO
archipelago
Daewoo.
Toronto