word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will." Middle English had self-witte "one's own knowledge and intelligence" (early 15c.).
OED counts 13 such compounds in Old English. Middle English Compendium lists four, counting the self-will group as a whole. It re-emerges as a living word-forming element mid-16c., "probably to a great extent by imitation or reminiscence of Greek compounds in (auto-)," and formed a great many words in the pamphlet disputes of the 17c.
1767, "a lowering of value" (originally of currency), noun of action from depreciate. Sense of "a belittling, deliberate underestimation of the merits of a person, action, or thing" is from 1790. Meaning "loss of value of a durable good by age or wear" is from 1900.
<a href="https://www.etymonline.com/word/self-depreciation">Etymology of self-depreciation by etymonline</a>
Harper, D. (n.d.). Etymology of self-depreciation. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/self-depreciation