dawn-n; 2 Senses

Sense Number 1: daybreak, time around sunrise

Commentary: DAWN[+event][+cyclic][+diurnal][+daybreak]

Examples:
They talked until dawn.
The pink light of dawn began to rise over the mountains.
The farmer got up before dawn to milk his cows.

Mappings:
PropBank: dawn.01
WordNet 3.0 Sense Numbers: 1, 2

Sense Number 2: beginning of an epoch or period of history characterized in some way

Commentary: DAWN[+time][+epoch][+beginning]
NOTE: a metaphoric extension of Sense 1

Examples:
These fossils date before the dawn of civilization.
That mission was at the dawn of the space age.

Mappings:
PropBank: dawn.01
WordNet 3.0 Sense Numbers: 3