*pete-

The original sense of the root was:

spreading, expanding

The most influential branch is probably the one around “pass” which is based on the idea of extending your leg to make a step. But there are other offspring as well.

Here’s an overview over the various English members of that family:

• pass (Originally: “taking a step”,  also to take a measure, so there’s a sense of the “expanse” in it)
• passage, passenger, passport
• expand, expansive (The root combined with the “ex”-prefix which here expresses “outward”)
• patent (Originally: “lying open” for an “open letter”)
• fathom (Originally a measure done by stretching out the arms, then shifted toward embracing, grasping)