For 1) and 2) I agree with Isi's response. "Monte" in spain can also refer to a general area with hills or mountains (for example "mi padre se ha ido al monte a cazar" - that doesn't mean he went to a mountain, but just to some area with nature, it could just be a forest or some hilly area) For 3) they're all similar, all cascara, piel and corteza are protective membranes. In my mind: - "cascara" is a hard surface that can crack (like a egg, or a walnut... in fact if you give 5 seconds to think about "cascara", everyone will say egg or walnut). - corteza is a a hard/rough/uneven surface that doesn't crack open like a cascara. Corteza de un arbol, is the most typical example. Also, corteza terrestre and corteza cerebral (Brain). Note how all those are not smooth, and don't crack like an egg or a walnut. - piel is for something that is not hard, like cascara or corteza. Usually smooth or furry. Piel de animales, de platano, de naranja, etc. There are cases which are borderline... for example I would say that a pineapple has corteza, and a watermelon has piel, but if someone used piel/corteza instead, it wouldn't necessarily strike me as too odd. Said all that... I don't think that with many of these synonyms you can derive a clear RULE to follow, because generally there isn't one, you just have to learn by looking at the examples and contexts where those words are used, and accept that there is a certain amount of overlap between synonyms.

Mhm well, I can tell you how it is for me. Hopefully I am not wrong :D 1. “Cama” would be the standard translation of the word “bed”. “Lecho” is a fancy translation of “bed” and it wouldn't be used in colloquial speech, unless you were trying to embellish your sentences for comedic purposes, or any other given reason. Examples. If someone told me “Ayer estaba echado en mi cama.” it wouldn’t sound odd to me But if someone said to me “Ayer estaba echado en mi lecho.” I would cringe haha 2. “Montaña” would translate as “mountain”, “colina” would be most properly translated as “hill”. and “monte” would translate as “mount”. “Montañas” are very high elevations of ground, usually rocky in appearance. Example, I would say that “The Alps are a set of “montañas”..” :D (Los Alpes son un conjunto de montañas) “Colinas” are usually very small elevations of ground, most common in fields. They tend to look smooth and green. Example, if we were at a field and there was a house on the top of a small elevation of ground, I would say “I bet a witch lives on that "colina" .." :) (Apuesto que una bruja vive encima de esa colina) It is hard for me to explain when I would use “mount”… I usually only use it for specific mountains, such as “Monte Everest”, “Monte Fuji”. To be honest, I hadn’t given it much thought, and now that I do, I don't know the answer... I’d advice to look these words up on google images so you can see the differences between them :) Images are pretty self-explanatory 3. This one if hard for me to explain and I do not want to give you any clumsy answers, it may confuse you even more.. I will let someone else take over this one! Hopefully I helped, if you have any questions, ask away