Reading is a fun pastime.
Spending your leisure time reading books for pleasure is an example of a pastime.
Origin of pastimeLate Middle English passe tyme, translated, translation of French passe-temps
Origin of pastimeMiddle English passe tyme, translation of French passe temps : passer, to pass + temps, time.
(third-person singular simple present pastimes, present participle pastiming, simple past and past participle pastimed)
From Middle English passe tyme, calqued on Middle French passe-temps.