Hola, a lo que yo entendí, según el diccionario de la RAE, primigenio y primitivo son sinónimos. Rocoso se refiere a un lugar que está lleno de rocas, o que tiene muchas rocas, y pétreo se refiere más a algo que tiene piedras o rocas o está hecho de estos materiales o con características o calidad de ellos. Hilo y hebra son sinónimos. Yo en lo personal utilizo la palabra "piedra" para referirme a rocas pequeñas o pedazos de roca. La palabra "roca" me hace imaginar un mineral de grandes dimensiones. Saludos.

Greetings Derek, well i'm going to try show you the difference, but that words are pretty similar between them. 1- "Primigenio" is used when you have the first state/model/transformation of something, like the very first nokia cellphone? the black and white one? "el celular primigenio de nokia", well something like that. meanwhile, "Primitivo" is more like an old model, it can be the very first model, or a model that is not the new one, like windows xp is primitive right now, but before xp there is windows 2000, windows 98, etc. "windows xp ya es primitivo hoy en dia". 2- "Pétreo" is more used in the science area, describing a material, it's more technical. "Un material de aspecto pétreo" "Rocoso" is more used to describe a place, rocky mountains for example. "El suelo es muy rocoso". 3- "Hilo" is more used when you are talking about clothes, cotton or construction materials, metal, etc. "Tu ropa se esta des-hilando" "Coloca un hilo de alambre de aluminio" "hebra" is more used in food, for example, when you take a pizza slice, and the cheese make a strand, "la hebra del queso" Tell me if you know the difference now. Sorry for my English, i'm still learning.

1. primigenio - relative to the origin or the begining . primitivo - belongs to the origin of a thing. (These can be synonyms) los dos términos son originarios, relativo al origen ej. En los tiempos primigenios había varias razas de hombres primitivos. 2. pétreo - made of stone , or it has the characteristics of a stone , hardness and texture rocoso - place full of rocks or rocky. Me quedé pétreo al divisar aquel paisaje rocoso. 3. hilo - A thread is a long thin strand of a textile material , especially used to sew hebra - Piece of thread , usually short , which is threaded into a needle to sew or embroider . (These can be synonyms) ¿Puedes enhebrarme este trozo de hilo para que pueda coser?