Ferrous is an adjective that means containing or consisting of iron. 

The Latin word ferrum (FAIR oom) means ‘iron.’ By the mid 19th century, this word had evolved into our word of the day as it came to describe anything made of iron. 

Those farrous bars on my window are intended to scare away any potential intruder. There’s something about the firmness of irons that makes dangerous people take notice.