IPA: /ˌpriːhɪˈstɒrɪk/
KK: /priˈhɪstərɪk/
Relating to the time before written history, often referring to ancient human cultures and their activities.
The museum has a fascinating exhibit on prehistoric animals and their habitats.
Prehistorical → It is formed from "pre-" (meaning before) and "historical" (from Greek "historikos", meaning relating to history). The word refers to the time period before recorded history.
Think of 'pre-' meaning before and 'historical' relating to history — so prehistorical refers to the time before history was recorded.