Noun
The word is derived from costa
The following five sets are known as " false ribs " (costae spuriae), three of these sharing a common cartilaginous connection to the sternum, while the last two (eleventh and twelfth ribs) are termed floating ribs (costae fluctuantes) or vertebral ribs. Source: Internet
The phrase true rib ( Latin costae verae main), or fixed rib, refers to the first seven, or vertebrosternal, rib pairs. Source: Internet