piling vs sheet piling

piling and sheet piling both are nouns.

Word	Noun	Adjective	Verb	Adverb
piling	Yes	No	No	No
sheet piling	Yes	No	No	No

As nouns, sheet piling is a hyponym of piling; that is, sheet piling 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
sheet piling: a pile in a row of piles driven side by side to retain earth or prevent seepage

Other hyponyms of piling include sheath pile, sheet pile.

piling (noun)	sheet piling (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