This is the 3653rd most frequent Russian word.
существенное
Essential.
used as an adjective meaning 'significant' to describe importance
Эта книга имеет существенное значение для понимания истории.
This book has significant importance for understanding history.
used as an adjective meaning 'essential' to describe a fundamental difference
Существенное отличие между этими теориями заключается в подходе к анализу.
The essential difference between these theories lies in the approach to analysis.
used as a noun referring to 'the essential thing' in the context of importance