Parsing the Reciprocal Example

Seven Semantic Functions of Form VI (Tafāʿul): Reciprocity, Multiplicity, Pretence, Response, Equivalence, and Independent Uses

تَشَاتَمَ زَيْدٌ وَعَمْرٌو
Translation: Zayd and ʿAmr exchanged insults.

WordSyntactic roleReason
تَشَاتَمَPast-tense verbStates the action
زَيْدٌNominative subjectThe action is assigned to Zayd
وَCoordinating particleJoins the two participants
عَمْرٌوCoordinated nominativeShares the subject's grammatical status

ʿAmr is not the accusative object in this construction. The coordination places him within the subject side of the sentence and suits the mutual meaning.