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yissus
Yizkor
-yl
ylang-ylang
yld
ylem
YMCA (1)
YMCA (2)
YMHA
Ymir
Ymodem
yo
yo-heave-ho
yo madd phat
yo-yo
yo-yo dieting
YOB
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yolk sac
yolk sac (plural yolk sacs)


noun 
Definition:
 
membrane surrounding embryo: a thin membrane surrounding the embryo in birds, fish, reptiles, and mammals. In birds, fish, and reptiles, it encloses the yolk.
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