Origin and history of developmental

1756, "a gradual unfolding, a full working out or disclosure of the details of something;" see develop + -ment. Meaning "the internal process of expanding and growing" is by 1796; sense of "advancement through progressive stages" is by 1836. 

Of property, with a sense of "a bringing out of the latent possibilities" for use or profit, from 1885 (Pickering's glossary of Americanisms, 1816, has betterments "The improvements made on new lands, by cultivation, and the erection of buildings, &c."). Meaning "state of economic advancement" is from 1902.

suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).