This is the 496th most frequent Turkish word.
geçmiş
"Geçmiş" means "past" in English.
Here, 'geçmiş' describes 'yıllarda' (years) and denotes a time period that has already occurred, serving as an adjective meaning 'past'.
Geçmiş yıllarda burada çok kitap okurdum.
In past years, I used to read many books here.
In this sentence, 'geçmiş olsun' is a set phrase used to wish someone recovery from illness or adversity, meaning 'may it pass away'.
Geçmiş olsun! Umarım yakında iyileşirsin.
Get well soon! I hope you recover quickly.
Here, 'geçmiş' acts as a verb in past perfect tense ('geçmiş'), implying something that has occurred or been concluded.