The Cu-O edge-sharing compound Li₂CuO₂, whose ferromagnetic chains are antialigned, is found from local spin density calculations to display several surprising characteristics: (1) the ordered moment/f.u. of 0.92 mu_B is the largest for any low dimensional cuprate system, in agreement with experiment, (2) 40% of this moment lies on the neighboring O ions, making it the largest oxygen moment yet reported, and (3) the second neighbors couplings are larger than nearest neighbors couplings. All of these phenomena arise naturally due to a well defined effective d_yz type orbital that includes very strong O p_sigma character. We interpret the large moment as surviving reduction by quantum fluctuations due to extension caused by the d-p hybridization.