アルミさん、さっき、ちょっと調べました。
定義の区別ができる可能性としては、
nature=substance=essence≠form=species
という具合ではないかなと。意味は以下のような感じ。
nature φύσις natura
substance ουσία substantia
essence ουσία essentia substantia
form φόρμα μορφή forma
species είδος species
http://archives.nd.edu/latgramm.htm natura -ae f. [birth; nature , natural qualities or disposition, character; an element, substance, essence]; 'rerum natura', [nature, the world or universe].
substantia -ae f. [substance , essence; property, means of subsistence].
forma -ae f. [form , figure, shape; beautiful shape, beauty; image, likeness; a shape serving as a model, e.g. a shoemaker's last; a mold, stamp
species -ei f.: act. [a seeing , view]; pass. [sight, look; shape, form, outward appearance; beauty; a vision, phantom; a representation, image, statue]. Transf. [pretext, pretence; notion, idea; kind, species].
http://www.perseus.tufts.edu/cgi-bin/resolveform φύσις (the nature, natural qualities, powers, constitution, condition)
ουσία (that which is one's own, one's substance, property)
μορφή (form, shape)
είδος (that which is seen, form, shape, figure)