the lock and key for a gate

to close and lock a gate

adder (viper)

a chain with a weight on one or both ends, such as might be used on a pulley to help lift loads / (weaponry) a Japanese martial arts chain weapon, consisting of or based on such a weighted chain

chainsaw

the Great Leap Forward

(history) the Nara period (710 - 794 CE)

an ice age (period of glaciation at the poles)

a historical period where social disorder is so great due to war, disease, political disorder etc. that there is little or no cultural development; Dark Ages

zeitgeist (the spirit of the age)