The Collaborative International Dictionary of English v.0.48:
Amerce \A*merce"\ ([.a]*m[~e]rs"), v. t. [imp. & p. p. Amerced
([.a]*m[~e]rst"); p. pr. & vb. n. Amercing.] [OF. amercier,
fr. a merci at the mercy of, liable to a punishment. See
1. To punish by a pecuniary penalty, the amount of which is
not fixed by law, but left to the discretion of the court;
as, the court amerced the criminal in the sum of one
Note: The penalty or fine may be expressed without a
preposition, or it may be introduced by in, with, or
2. To punish, in general; to mulct.
Millions of spirits for his fault amerced
Of Heaven. --Milton.
Shall by him be amerced with penance due. --Spenser.