tunic vs surcoat

tunic and surcoat both are nouns.

Word	Noun	Adjective	Verb	Adverb
tunic	Yes	No	No	No
surcoat	Yes	No	No	No

As nouns, surcoat is a hyponym of tunic; that is, surcoat is a word with a more specific, narrower meaning than tunic:

tunic: any of a variety of loose fitting cloaks extending to the hips or knees
surcoat: a tunic worn over a knight's armor

Other hyponyms of tunic include chiton, gymslip, kameez, kirtle, tabard.

tunic (noun)	surcoat (noun)
any of a variety of loose fitting cloaks extending to the hips or knees	a tunic worn over a knight's armor
an enveloping or covering membrane or layer of body tissue	a loose outer coat usually of rich material