decrease

[1]	diminish , reduce , decline , lessen , lower , abate , fall off , shrink , shrivel (up) , contract , dwindle , ebb , subside , wane , taper off , de-escalate , slacken , let up , ease (off/up) , curtail , cut (down/back) , (Colloq) run out of steam , (US) run out of gas
[2]	diminish , lessen , fall
[3]	lessen , minify

[1]	lessening , drop-off
[2]	decrement , diminution , reduction , decline , lessening , lowering , abatement , falling off , shrinking , shrivelling , contraction , decrement , dwindling , ebb , subsidence , tapering off , wane , de-escalation , slackening , easing (off/up) , curtailment , cut , cut-back
[3]	decrement
[4]	diminution , reduction , step-down