See lessen in Webster's New World Roget's A-Z Thesaurus II
verb
To grow or cause to grow gradually less:
abate, decrease, diminish, drain, dwindle, ebb, let up, peter (out), rebate, reduce, tail away (or off), taper (off). See increaseTo make less severe or more bearable:
allay, alleviate, assuage, comfort, ease, lighten2, mitigate, palliate, relieve. See increase
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