1590s, "very sparing in expenditure," from Latin parsimonia "frugality, thrift" (see parsimony) + -ous. Not originally with the suggestion of stinginess, but this had emerged by 18c. Related: Parsimoniously; parsimoniousness.
early 15c., parcimony, "economy, thrift, frugality, sparingness in the use of expenditure of means," from Latin parsimonia "sparingness, frugality, thrift," from pars-, past-participle stem of parcere "to spare, save, refrain from, use moderately" (which is said to be unrelated to Latin parvus "small," parum "too little") + -monia, suffix signifying action, state, or condition. De Vaan suggests a PIE source-word meaning "to hold." Now commonly "excessive or unnecessary economy, stinginess," a narrowed sense attested by mid-16c.
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."
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Harper, D. (n.d.). Etymology of parsimonious. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/parsimonious