verb

• (transitive) To carry (someone) on the back or shoulders.
• (transitive) To ride on someone's back or shoulders.
• (ambitransitive) To attach or append something to another (usually larger) object or event.
  "They tried to piggyback that proposal on the rivers and harbors bill."
• (transitive, Internet) To obtain a wireless internet connection by bringing one's own computer within the range of another's wireless connection without that subscriber's permission or knowledge.

noun

• (countable) A ride on somebody's back or shoulders.
• (medicine, countable, uncountable) The connection of one intravenous drip to another.
  "Piggyback medications are given through a port of an existing intravenous site. […] Calculation of the drip rate for piggybacks is the same as any other drip rate."