fibrinogen

noun

1. a protein present in blood plasma; converts to fibrin when blood clots

   noun.substance

   Synonyms factor i

   Source: WordNet 3.0

2. An albuminous substance existing in the blood, and in other animal fluids, which either alone or with fibrinoplastin or paraglobulin forms fibrin, and thus causes coagulation.

   noun

   Source: webster1913