Merriam-Webster's Collegiate Dictionary:
yellow poplar
yellow rain
yellow sea
yellow spot
yellow-dog
yellow-dog contract
yellow-fever mosquito
yellow-green alga
yellow-shafted flicker
yellowfin
yellowfin tuna
yellowhammer
yellowish
yellowknife
yellowlegs
yellowstone
yellowstone falls
yellowstone national park
yellowtail
yellowtail flounder
yellowtail snapper
yellowthroat
yellowware
yellowwood
yelp
yelper
yeltsin
yemen
yemeni
yemenite
yen
yen hsi-shan
yen-shee
yen-t'ai
yenan
yenisey
yenta
yeoman
yeoman of the guard
yeomanly
yeomanry
yep
yerba mat?
yerevan
yerk
yerkes
yes
yes-man
yeshiva
yeshivah
yesil irmak
yesilkoy
yester
yesterday
yesternight
yesteryear
yestreen
yet
yet again
yeti
yeuk
yevreyskaya
yevtushenko
yew
yezd
yezo
ygerne
yggdrasil
yhwh
yibin
yichang
yid
yiddish
yiddishism
yiddishist
yield
yielder
yielding
yikes
yin
yin and yang
yinchuan
yingkou
yingkow
yinglish
yining
yip
yippee
yippie
yips
yk
ylang-ylang
ymca
ymha
ymir
yo
yo-yo
