Abarim Publications' online Biblical Greek Dictionary
Hyssop is named after the Hebrew noun אזוב ('ezob), or at least any close relative of that ancient word, from which a great many languages of the world, including English, derive their words for soap. This is why David could exclaim: "Purify me with hyssop, and I shall be clean; wash me, and I shall be whiter than snow" (Psalm 51:7). It appears that, over time, the sponge or any sponge-like plant, became named after the soap, but since the stems of the plant we call hyssop today are about half a meter long and rather wobbly, one could hardly have served as the stalk upon which the sponge with vinegar (οξος, oxos) was hoisted toward the dying Christ (John 19:29).
John speaks of vinegar and hyssop, but Matthew of vinegar and χολη (chole), gall (27:34; Mark and Luke only mention vinegar, Mark 15:36, Luke 23:36). This suggests that in New Testament times, the word υσσωπος (hussopos) still denoted a liquid of some sort, perhaps taken from the plant that would later be known for its liquid. Something rather similar happened to the word מור (mor), or myrrh, from the verb מרר (marar), to be strong or bitter. The word οξος (oxos) comes from οξυς (oxus), meaning sharp, which reminds of the name Tigris, which denotes formal authority and legislation, and ultimately the beginning of complex civilization.