Merriam-Webster's Collegiate Dictionary:
y
y chromosome
y'all
y-axis
y-coordinate
y-intercept
y? shan
y?an shih-k'ai
ya
yabber
yabbie
yabby
yablonovy mountains
yablonovyy mountains
yabucoa
yacarana
yacht
yacht club
yachting
yachtsman
yack
yada yada
yada yada yada
yadda yadda
yadda yadda yadda
yadkin
yafo
yag
yagi
yahoo
yahooism
yahveh
yahweh
yahwism
yahwistic
yak
yakama
yakima
yakitori
yakutat bay
yakutia
yakutsk
yale
yalong
yalow
yalta
yalu
yalung
yam
yam kinneret
yamagata
yamal
yamamoto
yamashita
yamen
yammer
yamoussoukro
yampa
yamuna
yan'an
yana
yanam
yang
yang-chou
yangch?an
yangku
yangon
yangquan
yangtze
yangzhou
yank
yankee
yankee-doodle
yankeedom
yankeeism
yanomama
yanomami
yanomamo
yanqui
yantai
yantra
yao
yaound?
yap
yapese
yapper
yaqu?
yaqui
yar
yarborough
yard
yard goods
yard grass
yard line
yard sale
yard-long bean
yardage
