*(s)pen-

The core idea of this root was:

drawing (in length), stretching, spinning

The biggest group of English offspring is the branch based on the Latin word pendere, which meant to hang. Think of a weight hanging on a chord – the chord gets stretched. This was is how the family also took on the sense of weighing, and via weighing money (coins) it broadened to include the idea of payment.
Here’s an (incomplete) list:

• pending, pendulum
• perpendicular (“hanging of”, think of a chord hanging from the ceiling)
• depend (“hang of”)
• append (“hand onto”)
• suspend (“to hang under/away”)
• pound (“hanging weight”)
• compound (“hang together”)
• spend (originally: weighing money)
• expend, expensive (“pay out”)
• peso (“weight”, became the currency in Spain)
• compensate (“to weigh together – to get ballance”)
• pension (“payment”)
• penchant (“hanging toward a side”)
• ponder (“to weight in mind”)

Besides this group, there are also words like span, spider and spin.

The weirdest one is probably the German die Speise (meal) which evolved from the idea of “daily expenses”.