alteration, change, modification - an event that occurs when something passes from one state or phase to another; "the change was intended to increase sales"; "this storm is certainly a change for the worse"; "the neighborhood had undergone few modifications since his last visit years ago"

shrinkage, shrinking - process or result of becoming less or smaller; "the material lost 2 inches per yard in shrinkage"

casualty - a decrease of military personnel or equipment

sinking - a slow fall or decline (as for lack of strength); "after several hours of sinking an unexpected rally rescued the market"; "he could not control the sinking of his legs"

attrition - a wearing down to weaken or destroy; "a war of attrition"

dwindling, dwindling away - a becoming gradually less; "there is no greater sadness that the dwindling away of a family"

waning - a gradual decrease in magnitude or extent; "the waning of his enthusiasm was obvious"; "the waxing and waning of the moon"