"Quick service." One of the two servants of Ægir, the other being Eldir. In the prose introduction to Lokasenna it is told that during a feast hosted by Ægir, the guests praised much the ability of his servants. This greatly annoyed Loki and so he slew Fimafeng, whereupon the gods shook their shields and howled at Loki, and drove him away to the forest.
Fimafeng and Eldir are mentioned only in connection with this event.