cohercen, from Middle French cohercer, from Latin coercere "to control, restrain, shut up together," from com-"together" (see co-) + arcere "to enclose, confine, contain, ward off," from PIE *ark- "to hold, contain, guard" (see arcane). Related: Coerced; coercing. No record of the word between late 15c. and mid-17c.; its reappearance 1650s is perhaps a back-formation from coercion.
coercive (adj.)
c.1600, from coerce + -ive. Form coercitive (attested from 1630s) is more true to Latin.