One question: is there any reason for using different words meaning "leather"?
Why do I ask for this:
in Italian language we commonly use two different words for this material: "pelle" and "cuoio". The first litterally means "skin" while the second sounds much more like commercial leather. We use those words in different ways, frequently geographically varied from area to area but generally meaning "thin and/or softer leather" for word "pelle" and "thick and/or harder leather" for "cuoio".
Technically for both materials the term is "cuoio" but related to different acceptations they are used in different ways.
Isn't it the same in Greek?
In Greek we have δέρμα which is used for skin and commercial leather, and πέτσα (which comes from Italian pezza, love you guys!) which is more slangy for skin and leather also, πέτσινος=made of leather. But they don't have different meanings in Greek, both can be used with both meanings.
A more formal and medical term is the word "επιδερμίδα", that is the most elegant and sensitive part of the skin. A colloquial and vulgar word is πέτσα or πετσί, like the leather used for belts. Never use επιδερμίδα for belts :), better δέρμα or πετσί (pl. πετσιά). Πέτσα, a word even more colloquial and vulgar. All of them are δέρμα. But it depends on the case when you can use it:
Επιδερμίδα or δέρμα at the dermatologist's or cosmetics's stores.
Δέρμα but rarely πετσί (more colloquial) for belts.
Πέτσα, too colloquial, used only by old mountaineers.
The adjectives: επιδερμικός/η/ο, δερματικό/ή/ο, for scientific speech, δερμάτινος/η/ο, made of leather, πέτσινο/η/ο= a fake s'thing, i.e. πέτσινο φάουλ in soccer, colloquial and informal :)