What does abatement mean?
The definition of abatement
A*bate”ment, n.
Etym: [OF. abatement, F. abattement.]

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 thereof.
2 The amount abated; that which is taken away by way of reduction; deduction; decrease; a rebate or discount allowed.
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, want of jurisdiction) the proceedings should be abated.