Plane and plain are two words that are spelled differently, pronounced the same, and can share a meaning, namely a flat surface. Two questions:
Is there a term for word pairs like this?
Are there other similar word pairs?
I don't know about the "can share a meaning" bit, but:
homophone noun each of two or more words having the same pronunciation but different meanings, origins, or spelling, e.g., new and knew . • each of a set of symbols denoting the same sound or group of sounds.
also see:
homograph noun each of two or more words spelled the same but not necessarily pronounced the same and having different meanings and origins (e.g., bow 1 and bow 2 ). DERIVATIVES homographic adjective
So, maybe you need two words to express what you mean: "synonymous homophones" for example.
They
do both come from the same Latin word
Was just thinking about this one today and it is a little confusing!
Bartleby to the rescue:
A plain is “a broad, flat expanse of country,” and so the corresponding adjective means “level,” “lacking decoration,” “unpretentious,” and “uncluttered and obvious.” Used of persons, plain means “homely or lacking in beauty.” A plane is “a geometrically flat surface,” “a tool for smoothing wood to make it flat,” “a kind of tree,” and any of a number of specialized names for surfaces of like qualities, such as the planes of a glider or airplane. Plain and plane are homophones, but confusion can arise when you spell the name of the specialized flat surface you have in mind: is it a plane or a plain? Plain is topographical at the outset, and plane, geometrical, but from there on, your dictionary should be your guide. bartleby