decline

[1]	refuse , turn down , deny , reject , demur , forgo , veto , avoid , abstain from
[2]	diminish , lessen , decrease , wane , flag , go down , fall/taper off , subside , ebb , abate , dwindle , shrink , fade , (Colloq) peter out , run out of steam , (US) run out of gas
[3]	slope/slant (downwards) , descend , drop/fall off , dip , sink
[4]	deteriorate , degenerate , worsen , fail
[5]	go/drop down , worsen , settle , dip , sink , set
[6]	refuse , reject , pass up , turn down
[7]	refuse
[8]	go down , wane
[9]	slump , correct

[1]	diminution
[2]	declination
[3]	decay
[4]	descent , declivity , fall , declination , declension , downslope
[5]	diminution , decrease , lessening , ebb , downturn , fall-off , reduction , abatement , slump , descent
[6]	degeneration , deterioration , loss , diminution , weakening , debility , weakness , worsening , decay , failing
[7]	declivity , (downward) slope/slant , descent , downgrade , incline