Thank you all for your comments.

@Goofy: I read the bengali dictionary you had referred to. First it says that 'আগ্রাসন' is in noun form. Next it means "an intention (may be intention is not the right word, should be 'a state of having intention') to attack or conquer a foreign land". As aggression does not exactly coincide with what is written in Bengali, I guess it includes the English word 'aggression' to suggest that it is the closest possible match in English.

In the second part, it is written that 'আগ্রাসী' is the adjective form of 'আগ্রাসন'.

The dictionary, unfortunately, does not give any information about the origin of this word.

More specifically, I was actually trying to find whether or not আগ্রাসন (bengali meaning of aggression) is borrowed/derived from Sanskrit. Around 95% of Bengali words are either (re)borrowed from Sanskrit, or cognates of Sanskrit words. The rest are influenced by other languages, including Euroepan languages. Connection to English and other Euroepan languages are surely not uncommon because of colonial history. But if আগ্রাসন is a word that is derived/borrowed from Sanskrit, then such a resemblance would be surprising.

On the other hand, if it is simply borrowed from English, and developed in the last 300 years, I guess it resolves my confusion. But I do not have a proof of that either.

I am actually not an expert in this topic, and in fact I could even be wrong in my short description of the Bengali vocabulary; so if you can comment, I would highly appreciate it.