Correct spelling, explanation: the word entered English quite late as in the 19th century from Latin via French. The original Latin form was aggress and because of that today the word aggressive also features a double -g and a double -s letter in the middle, which for many users is quite a confusing spelling.

Definition of aggressive:
adjective – to behave in a violent way,
His dog is so aggressive that I’m afraid of entering his yard alone.
adjective – determined to win or achieve a goal really badly so that it requires violent or unfair means,
The presidential election was really aggressive and neither of the candidates was sure to win.
adjective – in medicine it refers to a condition that spreads quickly and leaves almost no chance of curing,
This type of cancer is so aggressive that patients who suffer from it live no longer than a year or two.

Collocations with aggressive:
Some typical collocations with the word aggressive include: seem aggressive, look aggressive, become aggressive, be aggressive towards, and openly aggressive.
He seems aggressive every time the topic of his ex-wife is on the table.
This dog looks aggressive so you’d better not touch him.
He becomes aggressive really quickly, which is rather worrying.
The dog is aggressive towards kids so be careful.
Her behavior at work starts to be openly aggressive.

Incorrect spelling, explanation: the word aggressive has quite an unusual spelling as there are two -g letters in the first syllable, which is rather uncommon in the English language. As a result, the form agressive is one of the most common mistakes made by both native users and learners of English.

Incorrect spelling