means The absolute lowest point of something — the bottom of a decline, the worst moment in a run of bad ones.

from From Arabic 'naẓīr' (as-samt), meaning 'opposite' — specifically the point in the sky directly opposite the zenith, straight down beneath your feet. Medieval astronomers borrowed it through Latin into the European languages, so the word arrived as a precise sky-mapping term before it ever meant rock bottom. Its high-flying twin, 'zenith,' comes from the same Arabic astronomical vocabulary — the two are a matched pair, the ceiling and the floor of the heavens.