Fierce- Adjective- having or showing a lot of strong emotion: very strong or intense
Fiercely- Adverb- 1) in a fierce or vehement manner
2) to a high degree: very
The word is used in the Shawl by Louise Erdrich which can find on the third paragraph.
When the uncle came around to fetch Aanakwad, in his wagon fitted out with sled runners, it was very hard, for she and her husband had argued right up to the last about the children, argued fiercely until the husband had finally given in.
Aanakwad and her husband had a strong argument about their children when the uncle of her lover came around to bring her. Finally she brought her daughter and left the son with the husband.
http://www.merriam-webster.com/dictionary/fiercely
