The Collaborative International Dictionary of English v.0.48:
Abatement \A*bate"ment\ (-ment), n. [OF. abatement, F.
1. The act of abating, or the state of being abated; a
lessening, diminution, or reduction; removal or putting an
end to; as, the abatement of a nuisance is the suppression
2. The amount abated; that which is taken away by way of
reduction; deduction; decrease; a rebate or discount
3. (Her.) A mark of dishonor on an escutcheon.
4. (Law) The entry of a stranger, without right, into a
freehold after the death of the last possessor, before the
heir or devisee. --Blackstone.
Defense in abatement, Plea in abatement, (Law), plea to
the effect that from some formal defect (e.g. misnomer,
lack of jurisdiction) the proceedings should be abated.