in the metric system, word-forming element denoting one-tenth of the standard unit of measure, 1801, from French deci-, taken arbitrarily from Latin decimus "tenth," from decem "ten" (from PIE root *dekm- "ten").
also metre, "fundamental unit of length of the metric system," originally intended to be one ten-millionth of the length of a quadrant of the meridian, 1797, from French mètre (18c.), from Greek metron "measure," from PIE root *me- (2) "to measure." Developed by French Academy of Sciences for system of weights and measures based on a decimal system originated 1670 by French clergyman Gabriel Mouton.
<a href="https://www.etymonline.com/word/decimeter">Etymology of decimeter by etymonline</a>
Harper, D. (n.d.). Etymology of decimeter. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/decimeter