congratulation (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.

gwerə-, Proto-Indo-European root meaning "to favor."

It forms all or part of: agree; bard (n.); congratulate; congratulation; disgrace; grace; gracious; grateful; gratify; gratis; gratitude; gratuitous; gratuity; gratulation; ingrate; ingratiate.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit grnati "sings, praises, announces;" Avestan gar- "to praise;" Lithuanian giriu, girti "to praise, celebrate;" Old Celtic bardos "poet, singer."