sorrow: the deep, inward grief of the heart, the lasting kind that quietly wears a person down
This word names sorrow felt on the inside: grief that settles in the heart and stays. It is not the public ritual of mourning with torn clothes and ashes (אֵבֶל), and it is not a sharp physical wound (מַכְאוֹב). It is the quiet, wearing sadness a person carries within, often for a long time, after loss or disaster.
The Bible keeps tying it to the slow eroding of a life. One psalm says "my life is consumed" by it and "my years" pass in sighing (Psalm 31:10); another feels it "in my heart" all day long (Psalm 13:2). It pairs again and again with sighing (אֲנָחָה), with distress, and with the hard toil (עָמָל) that produces it (Jeremiah 20:18). Later Jewish writers went so far as to say that grief like this can shorten a life. It is the sorrow that quietly uses a person up.
In the Hebrew, this grief is always something that comes upon a person from outside, never something they take up by choice. Jacob fears it will carry his gray head to the grave over a lost son (Genesis 42:38). Jeremiah names it as the whole weight of his calling as a prophet (Jeremiah 8:18; 20:18), and passes the same word to his scribe Baruch (Jeremiah 45:3). In Ezekiel it is even poured out as a punishment, the grief that fills a cup of judgment (Ezekiel 23:33).
Its steady opposite is joy, never merely relief or healing. That is why the prophets reach for this exact word to name the thing God promises to undo: "sorrow and sighing will flee away" (Isaiah 35:10; 51:11), and "I will turn their mourning into joy and give them gladness for their sorrow" (Jeremiah 31:13). Even the book of Esther, which never mentions God directly, borrows the phrase when the month is "turned from sorrow to joy" (Esther 9:22). It is at once Israel's deepest word for inner grief and the very grief the coming age is pledged to end.