I've noticed that many synonyms are often not very alike. Yes, their core meaning is the same. But there are many differences in mood or tone. Often I understand the kind of meaning it will have by the sound of it.
Here's how I interpret two synonyms 'happy' and 'glad'
Being happy reflects a positive attitude or nature as a general overall feeling. Just feeling the wind on my skin makes me happy. Life going on peacefully and smoothly makes me happy. Being carefree makes me happy.
Gladness requires more of a benefit to oneself. You're usually glad because something was done. It eases your life in some way or it simply makes you feel happy. Either ways, it was beneficial and that makes you glad.
"Skinny" and "Slender"
Skinny has a sharp tang. It adds to the quality of being thin sometimes a certain sexiness and sometimes (mostly in Old English) an unhealthy and unattractive connotation.
Slender has the same basic meaning as 'skinny', but it paints a more graceful and eloquent picture of thinness. I automatically associate slenderness with a refined sense of beauty.
I have never learnt it anywhere but still whenever I see these words being used, that is how I understand them. Why is it that way?
I know all of it looks very confusing. It does to me too. To be honest, I hardly understand what my question is myself. Hopefully, somebody will be able to sort this mess out and identify what I'm asking.