A bitter herb.

After this, Jesus knowing that all things were now accomplished, that the scripture might be fulfilled, saith, I thirst. Now there was set a vessel full of vinegar: and they filled a sponge with vinegar, and put it upon HYSSOP, and put it to his mouth. When Jesus therefore had received the vinegar, he said, It is finished: and he bowed his head, and gave up the ghost. ( John 19:28-30 )

Dictionary of Words from the King James Bible. Public Domain. Copy freely.