Merriam-Webster's Collegiate Dictionary:
mayflower
mayfly
mayhap
mayhem
maying
maykop
mayn't
maynooth
mayo
mayon
mayonnaise
mayor
mayoral
mayoralty
mayoress
mayotte
maypole
maypop
mayr
mayst
maytime
maywood
mayyali
mazaca
mazard
mazarin
mazatl?n
maze
mazel tov
mazelike
mazer
mazourka
mazowiecki
mazurka
mazy
mazzard
mazzini
mb
mba
mbabane
mbandaka
mbaqanga
mbd
mbe
mbeki
mbini
mbira
mbo
mbomou
mbps
mbs
mbuji-mayi
mc
mc-
mcadoo
mcallen
mcat
mcc
mccarthy
mccarthyism
mccarthyist
mccarthyite
mcclellan
mcclintock
mccloskey
mccloy
mcclure
mccormack
mccormick
mccoy
mccullers
mcdowell
mcfadden
mcg
mcgill
mcgovern
mcguffey
mcguffin
mcintosh
mcjob
mckeesport
mckenna
mckim
mckinley
mckinley, mount
mckinney
mcl
mcluhan
mcmahon
mcmillan
mcminnville
mcmurdo sound
mcnamara
mcnaughton
mcp
mcpo
md
