And sometimes we get it wrong -- very wrong ! But to be fair , there are simply some expressions that most native English speakers understand and use incorrectly . The problem with these terms is that , over the years , they have been shortened and important words are missing . That idiom is -- Blood is thicker than water . If I ask 100 people what the idiom means , most , if not all , will say that it means family relationships are the most important . The blood you share with your relatives represents a strong relationship . We call these family ties . "Water " here seemingly represents the connection you have with people with whom you do not share blood ties . And those links simply are not as strong . First , let's look at the word "thick ." In this idiom , it does not mean the physical size of something , as in the walls on the house are very thick . Here , the word "thick " means to have a very close relationship with someone . If you are thick with your best friend , you trust him . You could even say you guys are ‘tight .’ When used this way , "thick " gives us a few other idioms . If two friends are thick as thieves , they are very close and trust each other a lot . When you steal from others and get caught , you will probably go to jail . So , it is important to trust the people you steal with . If one rats out the others , you could all end up in jail ! The bond between thieves goes beyond a normal friendship . But for us non-thieving people , it's also important to be there for our friends . If you are a supportive friend , you see your friends through good times and bad . Another way to say this is to see them through thick and thin or be with them through thick and thin . So , the idiom blood is thicker than water means family ties are the strongest . That makes sense , right ? Well , it makes sense until you hear the whole idiom as it was first written in the Bible . The original saying is "Blood of the covenant is thicker than water of the womb ." The important words in the original version are the ones dropped over the centuries : "covenant " and "womb ." A "covenant " is a serious , official agreement or promise . Usually , we only use the word "covenant " when the agreement is important , such as a "covenant with God " or "the covenant of marriage ." Covenants often involve legal requirements , such as an "international covenant on human rights ." In our Bible-based idiom , the covenant is between soldiers on the battlefield . So , we don't use the term lightly . Now , the other important word is "womb ." A womb is the uterus , an organ where a woman carries an unborn baby . The water in the womb protects the fetus as it grows during pregnancy . And when a pregnant woman's water breaks , she will soon give birth . The English language has other idioms with the word "womb ." For example , womb-to-tomb means from birth to death . A tomb is a building above or below the ground where we keep dead bodies . We often use “womb-to-tomb ” when talking about government policies that protect a person for their entire life . Another way we say this is “from cradle to the grave .” A cradle is a bed for a baby . And a grave is a hole in the ground for burying a dead body . So , womb-to-tomb or cradle-to-grave are both ways to refer to a person's entire life but in a more dramatic way . And drama is probably what the rock band U2 was going for in their song “All I Want Is You .” Not only are we using "blood is thicker than water " incorrectly , the current usage is opposite from the original meaning . But here's the thing , we ALL use this idiom incorrectly . So , if you want people to understand your actual meaning , you may want to use it the way everyone else does . You mean , incorrectly ? Yes , I do . And then you can impress them with your knowledge of the original meaning of the idiom . That would be a great dinner party story . That's a great idea . And that's our program for this week . But it is not the end of the expressions that we use incorrectly . There are several of those .