WordNet (r) 3.0 (2006):

in extremis
    adv 1: at the point of death

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "in extremis":
   bad, between two fires, cornered, despaired of, desperate,
   done for, dying, endangered, expiring, facing death, given up,
   going, hard pressed, hard up, hopeless, imperiled,
   in a predicament, in articulo mortis, in danger, in desperate case,
   in desperate straits, in extremities, in jeopardy,
   incapable of life, jeopardized, low, moribund, near death,
   nonviable, on the spot, pinched, sinking, slipping, slipping away,
   sorely pressed, straitened, terminal, threatened, up against it



Bouvier's Law Dictionary, Revised 6th Ed (1856):

IN EXTREMIS. This phrase is used to denote the end of life; as, a marriage
in extremis, is one made at the end of life. Vide Extremis.