A.T. Robertson Commentary Revelation 8:11

"and the name of the star is called Wormwood: and the third part of the waters became wormwood; and many men died of the waters, because they were made bitter." — Revelation 8:11 (ASV)

Wormwood (ο Αψινθος). Absinthe. Usually feminine (η), but masculine here probably because αστηρ is masculine. Only here in N.T. and not in LXX (πικρια, bitterness, χολη, gall, etc.) except by Aquila in Pr 5:4; Jeremiah 9:15; 23:15. There are several varieties of the plant in Palestine.

Became wormwood (εγενετο εις αψινθον). This use of εις in the predicate with γινομα is common in the LXX and the N.T. (16:19; John 16:20; Acts 5:36).

Of the waters (εκ των υδατων). As a result of (εκ) the use of the poisoned waters.

Were made bitter (επικρανθησαν). First aorist passive indicative of πικραινω. Old verb (from πικρος, bitter), as in 10:9f. In a metaphorical sense to embitter in Col 3:19.