Now in the age of Semantic Search. How much it is important to mention the original keyword which is relevant for the content? I mean any page can get ranked if the contextual meaning is same for the original keyword.
Yeah, its true that if the contextual meaning remain the same then any page can get ranked. But in my opinion you must mention the original keyword in order to get ranked better. It can happen that the original keyword has much competition so you can't mention it in your header but you should mention the original keyword in meta description or body or tags.
Its highly necessary to mention the original keyword also you may not mention it in the header or meta but it is highly evident that you mention it in the content body.