Lessen, v. t. [imp. & p. p. Lessened; p. pr. & vb. n. Lessening.]
Etymology: [From Less, a. ]
To make less; to reduce; to make smaller, or fewer; to diminish; to lower; to degrade; as, to lessen a kingdom, or a population; to lessen speed, rank, fortune. Charity . . . shall lessen his punishment. Calamy. St. Paul chose to magnify his office when ill men conspired to lessen it. Atterbury.
Syn. -- To diminish; reduce; abate; decrease; lower; impair; weaken; degrade.
1 other Webster entry under this spelling
Lessen, v. i.
To become less; to shrink; to contract; to decrease; to be diminished; as, the apparent magnitude of objects lessens as we recede from them; his care, or his wealth, lessened. The objection lessens much, and comes to no more than this: there was one witness of no good reputation. Atterbury.
Shades of meaning
Fernald has no entry of its own for lessen; he lists it under abate, alleviate.
Where he writes about it:
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