Gen. 2:16-17 – this would have been the “only” meaning of the death promised by God to Adam “the day” he sinned. Comprehensive death means full and complete death: physical, spiritual (sin-death) and eternal. Death meant death – full and total death. There was no distinction between any aspect of death. If no intervention by God had been done (Gen. 3:21) then “the very day” Adam and Eve ate from the tree they would have experienced a comprehensive death: sin-death, died physically, and their physical death would have been the portal into an eternal sin-death separation from God in the Lake of Fire. The death threatened meant full death. The death promised was a comprehensive death.
[For a more in-depth study see eschatology “Study Series 3 What Happened in the Garden”]