ply

Concise Oxford English Dictionary © 2008 Oxford University Press:
ply1

▶noun (pl. plies)

• 1 a thickness or layer of a folded or laminated material.

• 2 each of a number of multiple layers or strands of which something is made. [in combination] four-ply.

– origin ME (in the sense ‘fold’): from Fr. pli, plier ‘to fold’, from L. plicare ‘to fold’.

Concise Oxford English Dictionary © 2008 Oxford University Press:
ply2

▶verb (plies, plying, plied)

• 1 work steadily with (a tool).

  ■ work steadily at (one's business or trade).

• 2 (of a vessel or vehicle) travel regularly over a route, typically for commercial purposes.

• 3 (ply someone with) provide someone with (food or drink) in a continuous or insistent way.

  ■ direct (numerous questions) at someone.

– origin ME: shortening of apply.