An Etymological Dictionary of Astronomy and Astrophysics

Prefix meaning “ten” and “ten times” used in terms belonging to the metric system.

Etymology (EN): From Fr. déca-, from L. deca-, dec-, from Gk. deka “ten;”
cf. Av. dasa “ten,” Mod.Pers. dah “ten,” Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Etymology (PE): Dekâ-, from Fr. as above.