stone age

Short definition from Wiktionary

Proper noun

1. 1
   Alternative letter-case form of Stone Age.
2. 2
   A broad prehistoric period during which humans widely used stone for toolmaking.
3. 3
   Any extremely primitive or undeveloped era.
4. 4
   The time a particular field was introduced and was in its earliest stages of development.

Adjective

1. 1
   Belonging in the Stone Age.