This is an old biblical idiom but still used. It refers to the lees (dregs, sediments) of wine or other liquids that settle in the bottom of the containing vessel if it is not disturbed. Hence, the idiom refers to someone or something that is at ease, not disturbed, or worried. Sometimes this also has reference to a false assurance.
(USA) To move extremely slowly. Molasses drips slowly anyway but add January cold and gravity, dripping uphill would be an impossibility, thereby making the molasses move very slowly indeed!
If a young man sows his wild oats, he has a period of his life when he does a lot of exciting things and has a lot of sexual relationships. for e.g. He'd spent his twenties sowing his wild oats but felt that it was time to settle down.
(USA) When people say that you can't squeeze blood out of a turnip, it means that you cannot get something from a person, especially money, that they don't have.
When people say 'don't teach your grandmother to suck eggs', they mean that people shouldn't try to teach someone who has experience or is an expert in that area.
If something is a tough nut to crack, it is difficult to find the answer or solution. When used about a person, it means that it is difficult to get them to do or allow what you want.
'Hard nut to crack' is an alternative.
When someone doesn't realise what is really happening or is not paying enough attention to events around them, you can tell them to wake up and smell the coffee.
If you have to walk on eggshells when with someone, you have to be very careful because they get angry or offended very easily.('Walk on eggs' is also used.)