dawn: the first light of day, the moment darkness begins to give way to morning
This word names the daybreak, the earliest light that comes before the sun itself is up. It marks a moment in time (things happen at dawn, or people wait until dawn), and it names the light itself, spreading over the hills and turning night to day.
Because dawn arrives on its own each day, whether or not anyone is watching, it became a favorite Hebrew picture for what is sure and unstoppable. Hosea says God will come to his people as certainly as the morning comes. Isaiah promises that rescue will break out like the dawn. The poets go further and treat the dawn almost as a living thing: it has wings that reach to the far side of the sea, it has eyelids that open at first light, and a singer can call out to it to wake up.
One famous line, the taunt against the fallen king of Babylon in Isaiah, calls him the shining one, son of the dawn. Later readers turned that title into the proper name Lucifer, but in Hebrew it is simply a poetic image drawn from the morning sky, not the name of a person or a spirit.
One occurrence, in Isaiah 47:11, is genuinely uncertain and may not belong to this word at all (see the note there).
Nuances
Whether the word at Isaiah 47:11 belongs to "dawn" (so the verse speaks of not knowing the disaster's origin or first rising) or to a separate look-alike root meaning to charm or conjure away (so the verse speaks of not being able to ward the disaster off by magic).
- contestedIt is the noun "dawn", used figuratively for the onset or source of the calamity; the verse says its dawning cannot be foreseen.; BDB, s.v. שַׁחַר
- contestedIt is a separate root meaning to charm or conjure away, so the verse says the calamity cannot be averted by magic.; HALOT, s.v. שׁחר