What is "synallagmatic"

Synallagmatic \Syn`al*lag*mat"ic\, a. [Gr. ?, from ? a mutual agreement, contract, fr. ? to exchange, negotiate with; sy`n with + ? to change.] (Law) Imposing reciprocal obligations upon the parties; as, a synallagmatic contract.
--Bouvier.

"expressing reciprocal obligations," from Greek synallagmatikos, from synallagma "a covenant, contract," from syn- "together with" (see syn-) + allagma "thing taken in exchange," from stem of allassein "to exchange, barter," from allos "another" (see alias (adv.)).\n

a. (context legal English) Imposing reciprocal obligations upon the party.