colloquy 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.

Proto-Indo-European root meaning "to speak."

It forms all or part of: circumlocution; colloquium; colloquy; elocution; eloquence; grandiloquence; interlocution; interlocutor; locution; locutory; loquacious; loquacity; loquitur; magniloquence; magniloquent; obloquy; soliloquy; somniloquy; vaniloquence; ventriloquism; ventriloquy.

It is the hypothetical source of/evidence for its existence is provided by: Latin loqui "to speak;" Old Irish ad-tluch- "to thank," to-tluch- "to ask;" Old Church Slavonic tloko "interpretation, explanation."