Heydad is a shout of excitement, particularly the joyful cry that accompanied the grape harvest or battle. The vintners would shout as they treaded the grapes; warriors would raise the shout in victory. It is an onomatopoetic word — the sound of the shout itself seems captured in the word. The LXX renders it as a battle cry or harvest shout.
Judgment oracle passages in Jeremiah and Isaiah use the absence of heydad as a sign of catastrophic loss: when the joyful harvest shout is silenced, devastation has come. Conversely, this word teaches that work and worship were united in ancient Israel — the harvest shout was simultaneously a shout of thanks to God. In Jeremiah 25:30, God Himself thunders with a heydad against the nations — the divine warrior raising His own battle shout over fallen idols. Joy and judgment, praise and power, are not opposites.