contusion (n.)

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.

early 15c., "dull, blunted, not sharp," from Latin obtusus "blunted, dull," also used figuratively, past participle of obtundere "to beat against, make dull," from ob "in front of; against" (see ob-) + tundere "to beat," from PIE *(s)tud-e- "to beat, strike, push, thrust," from root *(s)teu- "to push, stick, knock, beat" (source also of Latin tudes "hammer," Sanskrit tudati "he thrusts"). Sense of "stupid, not acutely sensitive or perceptive" is by c. 1500. In geometry, in reference to a plane angle greater than a right angle," 1560s. Related: Obtusely; obtuseness.

"apt to cause a contusion, bruising," 1798, from Latin contus-, past participle stem of contundere "to beat, bruise, grind, crush, break to pieces" (see contusion) + -ive.