Where does “thoracic” come from?

Thoracic derives from Ancient Greek θωρακικός, an adjective form of Ancient Greek θώραξ meaning breastplate or chest.

thoracic (English): Of the thorax; One of a group of fishes having...

Definitions

thoracic traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Ancient Greek	θωρακικός	suffering in the chest, of the thorax
2	Ancient Greek	-ικός	of or pertaining to, in the manner of; -ic
3	Ancient Greek	-κός	forms adjectives with the sense of 'of or...
4	Proto-Indo-European	-ḱos	-y, -ic

Step	Language	Word	Meaning
1	English	thorax	The region of the mammalian body between the neck...
2	Latin	thōrax	chest, thorax
3	Ancient Greek	θώραξ	corselet; linen jerkin; coat of mail, cuirass