corroborate (v.)

word-forming element usually meaning "with, together," from Latin com, archaic form of classical Latin cum "together, together with, in combination," from PIE *kom- "beside, near, by, with" (compare Old English ge-, German ge-). The prefix in Latin sometimes was used as an intensive.

Before vowels and aspirates, it is reduced to co-; before -g-, it is assimilated to cog- or con-; before -l-, assimilated to col-; before -r-, assimilated to cor-; before -c-, -d-, -j-, -n-, -q-, -s-, -t-, and -v-, it is assimilated to con-, which was so frequent that it often was used as the normal form.

1540s, of persons, "having or indicating great strength, muscular, vigorous," from French robuste (14c.) and directly from Latin robustus "strong and hardy," literally "as strong as oak," originally "oaken," from robur, robus "hard timber, strength," also "a special kind of oak," named for its reddish heartwood, from Latin ruber "red" (related to robigo "rust"), from PIE root *reudh- "red, ruddy." Related: Robustly; robustness; robusticity.

Robustious (1540s) was an elaborated form common in 17c. (see "Hamlet" iii.2), with more of a sense of "rough, violent, rude;" according to OED it fell from use by mid-18c., but was somewhat revived by mid-19c. antiquarian writers. Related: Robustiously; robustiousness.