The phrase "blood is thicker than water" means that family bonds are stronger and more important than other relationships. 

The origin of this phrase is somewhat complex, as it has evolved over time and has different interpretations in various contexts. The phrase as we know it today is believed to have originated from a German proverb, "Blut ist dicker als Wasser," which directly translates to "blood is thicker than water." This suggests that family ties are stronger than other connections. 

There are variations of the phrase in historical texts. For example, in the 12th century, the German poet Heinrich der Glîchezære wrote a variant in "Reynard the Fox," which included a sentiment that "kin-blood is not spoiled by water." This implies that family blood bonds are enduring and strong. Some scholars argue that the original meaning of the phrase may have been different from its modern interpretation. 

An earlier version found in the 12th-century writings of the theologian and philosopher John of Salisbury stated, "Blood of the covenant is thicker than the water of the womb." This interpretation suggests that bonds formed by mutual commitments (such as friendship or loyalty) can be stronger than those formed by mere biology. By the 19th century, the phrase had evolved into its current form and meaning. Sir Walter Scott used it in his novel "Guy Mannering" (1815), which helped popularize it in the English-speaking world: "Weel, blude's thicker than water; she's welcome to the cheeses."