Galacto, lacto, galaxy

Gr. Gala : Milk (genitive; galakta) -->Gr. galaktikos (milky)
...........................................-->L. galaxia (Milky way; Via Lactea)
L. Lac : Milk (genitive; lactis) (Fr Lait)



lactation : Suckling
lactose: Milk sugar; < Lact + ose (sugar suffix; hexose, pentose, triose, glucose...)
lactic acid: Milk acid; an acid obtained from sour milk
galactose: Brain sugar; a constituent of lactose
galactin: prolactin