a temporary state of the dead in Roman Catholic theology
in some poems, such as "Mental Cases", Owen reveals the soldiers to be suffering in a half light or hell, where they are neither living or dead, and cannot cope with the sin or guilt of the murders they have committed under war.
'shell on frantic shell' is an example of the panicked emotion that was experienced in the dug out in the Sentry, where the men are enduring the constant stress of battle.
In S.I.W, Owen sardonically refers to the woman who don't comprehend what the men are going through, and hope they return with a 'safe wound to nurse' - hardly a realistic expectation give the fatalities and injuries suffered.