"Growing." A practitioner of seiðr, attested in Skáldskaparmál. She offered to remove the shard of whetstone lodged in Thor's head after his fight with Hrungnir. As she sang her spells, the whetstone began to loosen. Thor desired to reward her and make her glad, and so he told her about his encounter with her husband Aurvandil the Valiant, saying that it would not be long ere he came home. Gróa was so rejoiced that she forgot her incantations, and the whetstone stayed permanently embedded in Thor's head. Therefore it was forbidden to cast a whetstone across the floor, for then the hone is stirred in Thor's head, causing him considerable discomfort.
Þjóðólfr of Hvinir made a song after this tale in the Haustlöng.
- Skáldskaparmál, 25.