I'm looking for a method, a function or an API which checks whether a character string has a semantics or not (represents a word that has a meaning or a random letter string)
Python supports a special data structure called "dictionary" that deals with your question. Check: https://www.w3schools.com/python/python_dictionaries.asp.
There you'll even find examples of use of dictionaries in a function.
If some string is not in a dictionary, this could be because of a typo. I would use some Levenstein or other orthoneibourhood to check the neighbors too.