to use / to employ / to make use of, to apply / to spend

(archaic) iron / (figuratively) something extremely strong

(archaic) antique, old-fashioned / (colloquial) ancient

ancient times, antiquity, remote ages

iron

iron, the metal and the metallic chemical element / (more generally) steel / short for 鉄砲 (teppō, literally “cannon”, but in this case, refers to the poisonous fugu blowfish or dishes made from it)

use one thing for many purposes / work someone hard

to use one's head

the ancients, ancient people

Synonym of 始生代