厚道(hòudao) Honest and kind; Decent and magnanimous  

The origin of the word
The word 厚道(hòudao) comes from a sentence "做人要厚道(zuòrén yào hòudao) one should be honest and kind." a famous line from the movie Cell Phone 手机(shǒujī) in 2003. Since the movie was released, the word has been widely used in China.

The meaning of the word
厚道(hòudao) means treating others kindly and honestly. 厚(hòu) means thick in its literal sense, but here it means the quality of being kind and generous. And 道(dào) literally means the way or the road, but in the phrase 厚道(hòudao) refers to the manner people treat others. Thus, the phrase 厚道(hòudao) means being mild and good in nature.

The usage of the word
e.g.  1. 她最大的特点是为人厚道。
             Tā zuìdà de tèdiǎn shì wéirén hòudao.
             Her greatest attribute is her kindness.
         2. 他待人那么厚道，我们永远不会忘记他。
              Tā dàirén nàme hòudao, wǒmen yóngyuǎn bú huì wàngjì tā.
              He is so kind to others that we will never forget him.

低调(dīdiào) Keep a low profile  

Origin and Meaning
The word "低调(dīdiào) keep a low profile" comes from a sentence "高调做事，低调做人。(Gāodiào zuòshì, dīdiào zuòrén.) Work in high profile and behave in a low profile." Another sentence also shares the same meaning: "竖起桅杆做事，砍倒桅杆做人。(Shùqǐ wéigǎn zuòshì, kǎndǎo wéigǎn zuòrén.)" It means when you catch fish on the sea, you can put up the mast to speed up your ship and when you encounter the storm, you can cut it off to survive.
"低(dī)" usually means low which is used to describe a position, a level or a degree, but in the word 低调(dīdiào) it also refers to something inconspicuous. And "调(diào)" as a noun, can be used to refer to the melody and tune of music. While here it refers to someone's profile and image. 低调(dīdiào) means you should be modest and prudent toward people and you should not make a show of your ability in front of others. So when there are people who tend to flaunt themselves in public, we can say "You should 低调(dīdiào) keep a low profile."

Usage of the Word
e.g. 1. 我们在整个事件中必须保持低调。
            Wǒmen zài zhěnggè shìjiàn zhōng bìxū bǎochí dīdiào.
            We must keep the whole thing in a low profile.
       2. 他这人一直很低调。
            Tā zhè rén yìzhí hěn dīdiào.
            He always keeps a low profile.