What does commutation mean?

Back in 1780, Congress, responding to Washington’s appeals, voted that all officers who continued to serve until the end of the war should receive half pay for life.  In 1783, Congress adopted the “Commutation Act,” which changed the arrangement to five years full pay in money or interest bearing securities.  But because of a shortage of funds, the Confederation couldn’t pay the principal or the interest.  Speculators capitalized when Congress later provided payment of the certificates.  One of Joseph Howell’s duties at the office of Army accounts was verifying appropriate documentation for commutation claims.