• Gel(-mek) → to come (the root),
• Gelen → incoming (adjective),
• Gelenek → tradition (the customs or beliefs that come from old generation to new ones) (noun)
PS: the suffix "-ek" is one of the suffix that used to obtain a noun out of an adjective. More examples:
• olan → olanak,
• gören → görenek,
• düzen → düzenek.
How would you say “that traditional newspaper”?
Şu geleneksel gazete. - That traditional newspaper.
Demonstrative pronouns - "İşaret zamirleri."
Bu - This(one) Şu - This(one), that(one) O - That(one) Bunlar - These. Şunlar - These, those. Onlar - Those.