Mitigate, v. t. [imp. & p. p. Mitigated; p. pr. & vb. n. Mitigating.]
Etymology: [L. mitigatus, p.p. of mitigare to soften, mitigate; mitis mild, soft + the root of agere to do, drive.]
1. To make less severe, intense, harsh, rigorous, painful, etc.; to soften; to meliorate; to alleviate; to diminish; to lessen; as, to mitigate heat or cold; to mitigate grief.
2. To make mild and accessible; to mollify; -- applied to persons. [Obs.] This opinion ... mitigated kings into companions. Burke.
Syn. -- To alleviate; assuage; allay. See Alleviate.
Shades of meaning
Fernald has no entry of its own for mitigate; he lists it under abate, alleviate, amend, palliate.
Where he writes about it:
Assuage is, by derivation, to sweeten; mitigate, to make mild; moderate, to bring within measure; abate, to beat down, and so make less. — from alleviate
We abate a fever; lessen anxiety; moderate passions or desires; lighten burdens; mitigate or alleviate pain; reduce inflammation; soften, assuage, or moderate grief; we lighten or mitigate punishments; we relieve any suffering of body or mind that admits of help, comfort, or remedy. — from alleviate