cogent (adj.) Look up cogent at Dictionary.com
1650s, from French cogent "necessary, urgent" (14c.), from Latin cogentem (nominative cogens), present participle of cogere "to curdle; to compel; to collect," literally "to drive together," from com- "together" (see co-) + agere "to set in motion, drive, drive forward; to do, perform" (see act (n.)).