Achoach is a proper noun referring to a family or clan name — the Ahohite — from which several of David's mighty warriors descended. The name appears as a clan designation in genealogies and warrior lists.
The Ahohite warriors — including Dodo's son Eleazar (one of the three chief mighty men) and Ilai the Ahohite — represent a fascinating thread in the narrative of David's kingdom. These were men of extraordinary valor who defended the covenant king at great personal cost. Eleazar's stand against the Philistines when all other Israelite soldiers fled — fighting until his hand grew tired and 'froze to the sword' — is one of Scripture's great military narratives (2 Samuel 23:9-10). The LORD gave a great victory through one committed man. These warrior genealogies remind us that faithfulness to God's king (David as type of Christ) requires the same stubborn, costly commitment from those who would be numbered among His mighty men.