piling vs sheath pile

piling and sheath pile both are nouns.

Word	Noun	Adjective	Verb	Adverb
piling	Yes	No	No	No
sheath pile	Yes	No	No	No

As nouns, sheath pile is a hyponym of piling; that is, sheath pile is a word with a more specific, narrower meaning than piling:

piling: a column of wood or steel or concrete that is driven into the ground to provide support for a structure
sheath pile: a pile in a row of piles driven side by side to retain earth or prevent seepage

Other hyponyms of piling include sheet pile, sheet piling.

piling (noun)	sheath pile (noun)
a column of wood or steel or concrete that is driven into the ground to provide support for a structure	a pile in a row of piles driven side by side to retain earth or prevent seepage