I.to join or help in doing, τί τινι Aesch., Eur., etc.; ς. τινὶ τἀγαθά to assist one in procuring what is good, Arist.: —c. acc. rei only, Soph.; ς. εἰρήνην to help in negotiating peace, Xen.; c. dat. pers. only, to act with, cooperate with, τινί Thuc., etc.
2.absol. to lend aid, cooperate, Soph., Xen., etc.; οἱ ξυμπράσσοντες the confederates, Thuc.
II.intr., σὺν κακῶς πράσσοντι συμπράσσειν κακῶς to share in another's woe, Eur.
III.Mid. to assist in avenging, συνεπρήξαντο Μενέλεῳ τῆς Ἑλένης ἁρπαγάς Hdt.