expression, zuru verb
commute a death sentence to life imprisonment
Formal legal phrase; used in criminal law contexts. The verb 減ずる is a literary/formal alternative to 減じる.
裁判所は情状を考慮し、死一等を減ずる判決を下した。
The court, taking the circumstances into consideration, handed down a ruling commuting the death sentence to life imprisonment.
減刑 is a general term for reduction of a sentence, while 死一等を減ずる specifically refers to commuting a death sentence to life imprisonment.
Compound of 死 (death) + 一等 (one degree) + を (object marker) + 減ずる (to reduce). The phrase literally means 'to reduce the death penalty by one degree', i.e., to life imprisonment.