prosecution n.

1560s, "the carrying out or following up of anything" (also literal, "action of pursuing, a following after," but this is obsolete), from French prosecution (late 13c.) and directly from Late Latin prosecutionem (nominative prosecutio) "a following," noun of action from past-participle stem of prosequi "to follow after; chase, pursue; attack, assail" (see prosecute). The meaning "legal action, the institution and carrying out of a suit at law" is from 1630s. Hence, transferred, "the party by whom legal proceedings are initiated" (1891).