adjective
or sin·a·lag·mat·ic |sinə|lag|mad.ik, sə̇|naləg-
Etymology: Greek synallagmatikos of a contract, from synallagmat-, synallagma contract, covenant (from synallassein to enter into a contract, from syn- + allassein to change, exchange, barter, from allos other) + -ikos -ic — more at else
: imposing reciprocal obligations and characterized by mutual rights and duties : bilateral
synallagmatic contract
— sometimes distinguished from commutative ; compare commutative contract