Compare with the synonymous "survive" in this list: both verbs are used in this example sentence, and both example sentences use the verbs to emphasize the need for water. The Latin root of "endure" connects closely to hardship ("durare" means "to harden"), while "survive" connects more closely to life ("vivere" means "to live").
But here in the desert, nothing green could survive except tiny evergreen acacia bushes, which somehow endured the long winter months with almost no water.
The given definition makes "relentless" synonymous with "eternal" (both mean "never-ending"). But "relentless" also means "not to be appeased or moved by entreaty"--this would make the sun seem like an uncaring god who is not answering the people's prayers for relief.
The sun was relentless and eternal: There was neither wisp of cloud nor whiff of breeze for relief.
"Hollow" also means "devoid of significance or point"--this could describe the dying men's outlook on life, but the example sentence focuses more on the physical hollowness of the eyes that is due to a lack of water and food.
Salva looked at the hollow eyes and the cracked lips of the men lying on the hot sand, and his own mouth felt so dry that he nearly choked when he tried to swallow.
Compare with "survive" in this list--both come from the Latin verb "vivere" but "re" means "again" while "super" means "over" so reviving, as supported by this example sentence, is often seen as more miraculous than surviving.
Like a miracle, the small amounts of water revived them.
Compare with "din" in this list--the nouns are synonymous, but "clangor" is an onomatopoeic word that sounds like metal, while "din" can be any mixture of loud or confusing noises. Both words usually have an unpleasant sense, which would be true for a screaming crowd and pouring rain, but here, "clangor" connects to the friendly verb "greet" and to the voices of working men and women shouting and singing.
The clangor of machinery and hammer greeted Nya each time she returned from the pond—unfamiliar noises that mingled with the voices of men shouting and women singing.
"Mercy" means "a disposition to be kind and forgiving"--the use of the adjective "merciless" personifies the river (similar to how "relentless" can make the sun seem like a god); this makes the refugees' situation seem worse, since on one side, they have soldiers with guns, and on the other, they have a river--both of which are mean enough to kill.
Swollen by the rains, the Gilo’s current would be merciless.
As a verb, "welter" has more of a connection to water: "toss, roll, or rise and fall in an uncontrolled way, usually because of high seas"--although the example sentence uses the word as a noun, the verb is also suggested because the welter of arms and legs, tossed by the mad current of the river, is rising and falling as the people are trying not to drown, be shot, or eaten by crocodiles.
The rain, the mad current, the bullets, the crocodiles, the welter of arms and legs, the screams, the blood...