Same word as rail in:

apprehend, bastille, bottle up, cage, check, circumscribe, closet, commit, constrain, curb, detain, fence in, hold, hold captive, hold hostage, hold in custody, ice, immure, impound, incarcerate, intern, jail, keep, keep captive, keep in custody, limit, lock in, lock up, nab, occlude, pen, put away, put behind bars, rail in, remand, restrain, send to prison, send up, shut in, stockade, take prisoner, trammel