Q: I was on a hike in Manhattan with the Urban Rangers and had a dispute about the word “amphibian.” I said “amphi” means both, so an amphibian is comfortable on land and water. Another hiker insisted “ambi” (as in “ambidextrous”) means both, so “amphi” couldn’t. I dropped the subject, since I wanted to hear the guide discuss the geology of Inwood Hill Park. An interesting note: Fordham in the Bronx has a lot of gneiss and Inwood Hill a lot of schist. Or, as the guide put it, “Fordham is gneiss, but Manhattan is full of schist.”
A: Thanks for the interesting geology lesson.
As for "ambi" and "amphi," the two of them are Latin prefixes meaning both, around (that is, both sides), or about. They're derived from the Greek prefix amphi, which has the same meanings.
So, for example, "amphibian" means having two kinds existence, and "ambidextrous" means able to use both hands with equal ease.
Interestingly, the first citation for “amphibian” in the OED, from 1637, uses the term in a figurative way to refer to some doubtful characters in ancient Rome: “A certaine Amphibian brood, sprung out of the stem of the Neronian tyranny.” The term wasn’t used for reptiles until the mid-19th century.
The first published reference for “ambidextrous,” from 1646, is a comment about “ambi-dextrous and left handed men.”