What is Aggravation?

Legal Definition
Aggravation, in law, is "any circumstance attending the commission of a crime or tort which increases its guilt or enormity or adds to its injurious consequences, but which is above and beyond the essential constituents of the crime or tort itself."

Aggravated assault, for example, is usually differentiated from simple assault by the offender's intent (e.g., to murder or to rape), the extent of injury to the victim, or the use of a deadly weapon. An aggravating circumstance is a kind of attendant circumstance and the opposite of an extenuating or mitigating circumstance, which decreases guilt.

In the UK, the Criminal Justice Act 2003 requires a court to consider (a) relevant previous convictions, (b) racial or religious aggravation, and (c) hostility towards the victim or to persons generally based on sexual orientation (or presumed sexual orientation) or disability (or presumed disability) when determining sentence for a conviction.

The antonym of aggravation is mitigation.
-- Wikipedia
Legal Definition
Crimes, torts. That which increases the enormity of a crime or the injury of a wrong. The opposite of extenuation.

2. – When a crime or trespass has been committed under aggravating circumstances, it is punished with more severity; and, the damages given to vindicate the wrong are greater.
-- Bouviers Law Dictionary
Legal Definition
In pleading. The introduction of matter into the declaration which tends to increase the amount of damages, but does not affect the right of action itself. Steph. Pl. 257; 12 Mod. 597. See 3 An. Jur. 287, 313. An example of this is found in the case where a plaintiff declares in trespass for entering his house, and breaking his close, and tossing his goods about; the entry of the house is the principal ground and foundation of the action, and the rest is only stated by way of agravation; 3 Wils. R. 294; and this matter need not be proved by the plintiff or answered by the defendant.
-- Bouviers Law Dictionary
Legal Definition
Any circumstance at-tendfug the commission of a crime or tort which increases its guilt or enormity or adds to its Injurious consequences, but which is above and beyond the essentiui constituents of the crime or tort itself. Matter of aggravation, correctly understood, does not consist m acts of the same kind and description as those constituting the gist of the action, but in something done by the defendant, on the occasion of committing the trespass, which is, to some extent, of a different legal character from the principal act complained of. Hathaway v. Rice, 19 Vt. 107. In pleading. The introduction of matter into the declaration which tends to increase the amount of damages, but does not affect the right of action itself. Steph. PI. 257; 12 Mod. 507.
-- Black's Law Dictionary
Legal Definition
That which enhances the gravity of a criminal or tortious act; allegations in a declaration which tend to enhance damages. See 19 Vt. 107.
-- Ballentine's Law Dictionary