You would really need to give us more details about the topic of the poem or even just the Y line for us to be helpful but I can list a few words that start with Y for you:
YACHT
YACK
YAHOO
YAM
YANK
YAPPY
YARD
YARDLAND
YARDSTICK
YARN
YAWL
YAWN
YEAST
YELLOW
YELP
YES
YIELD
YODEL
YOLK
YOU
YUMMY