bookshelfnoun (pl bookshelves)

• substitute
• substrate
• substratum
• substructure
• subsume
• subtenant
• subtend
• subterfuge
• subterminal
• subterranean
• subtext
• subtilize
• subtitle
• subtle
• subtlety
• subtonic
• subtopia
• subtotal
• subtract
• subtraction
• subtrahend
• subtropic
• subtropical
• subtropics
• subulate