not only.. but also; as well as
Connects two clauses to say 'not only A, but also B', often with an unexpected or additional point.
This pattern emphasizes that the second item is also true or happens, going beyond the first. It's like saying 'not only... but also...'. The first part can be something expected, and the second part adds something extra or surprising. For example, if someone is smart (which is good) and also works hard (which adds more), you can use this pattern.
It works with verbs, adjectives, and nouns. For verbs, use the dictionary form. For nouns and な-adjectives, just place them directly before ばかりでなく. For い-adjectives, use the dictionary form as well. This pattern is slightly formal and common in written Japanese or speeches, but also used in spoken Japanese to make a strong point.
Note that the second clause often ends with も to emphasize 'also'. The pattern can be used with positive or negative things. In casual conversation, you might hear だけでなく instead, which is less formal.