If you read massively in a second or in a foreign language, you’re making up a tank of words, which will flow out when writing or speaking; maybe words you saw just once!
This happened to me recently, with the word “impoverished”. I wasn’t aware I had learned that word before.
Perhaps it was part of my passive vocabulary.
The active vocabulary is the one you can use.
The passive vocabulary is the one you can understand when reading, but you don’t use it.
Memory can be trained, more if you're learning a foreign or second language. / Photo from: autumn-5 www playbuzz com