The first time a solar flare was OBSERVED (as far as we know), was in 1859 by Carrington and Hodgson, who independently "discovered" flares; they described the flare as brilliant or intensely bright. According to a paper by E.W. Cliver that appeared in volume 157, 1995 edition of Solar Physics, the terms used in the 30s and early 1940s to describe these events on the Sun were eruptions or bright chromospheric eruptions. Interestingly, the first time that a flare was observed on a star other than the Sun was in the 1920s, with the best known seen in the late 1940s. But it seems that the first time the term "solar flare" was used, was in the 1940s. During the 1940s, the use of the term flare became more common, because observations of flares showed very little outward explosive movement. To see an abstract and first page of Cliver's paper, which describes the evolution of solar flare names, go to:
http://www.springerlink.c...nt/rj072005x602q675/
To see what Carrington and Hodgson actually wrote, go here:
http://www.ips.gov.au/Educational/2/4/4