The word resilient is used to talk about a particular kind of strength. When used to describe objects or materials, resilient means "returning to original form after being bent or stretched." In discussion of people, resilient conveys a buoyancy in the face of hardship or misfortune. A person who readily recovers or bounces back from adversity, illness, depression, or other types of difficult circumstances may be described as resilient. More commonly, resilient is used in discussion of systems and organizations, such as economies, communities, and cities, and increasingly, we see resilient in the descriptor phrase climate resilient, signifying the readiness and capability of systems and organizations to adapt to changing climate conditions.
Help comes in many different forms. To bolster something is "to add to, support, or uphold" that thing. The verb comes from the noun bolster, a cushion or pillow. The idea of cushioning, propping up, or giving a boost is central to the verb. However, while this noun bolster is most likely to prop up a person, the verb bolster is more commonly found in discussion of concepts and ideas. For example, you might bolster a case or an argument, or bolster a friend's confidence. Similarly, internet companies will seek to bolster their traffic, and government agencies strive to bolster the economy.
The most general feeling of sorrow or unhappiness can be captured with the adjective sad. The word bitter, on the other hand, describes a more pointed feeling, often one of disappointment, sharpened by resentment, hostility, or cynicism. A bitter sorrow is one that is deeply grievous or hard to bear. A bitter lesson is one that is hard to accept. And bitter rivals are competitors whose relationship is marked by intense antagonism or hostility. In all of these, you can find traces of bitter's earliest sense in English: "having a harsh or disagreeable taste."