Can I add my own synonyms to the library

I’ve noticed that many words don’t seem to have synonyms attached to them, is there any way to add your own to the library in the same manner you can add new words to it? LO 6.4 OS Win 10

in the same manner

Which manner is the same manner for you?

Sorry for the delay in answering either there was no notification or I’ve missed it. Either way, my apologies for not replying sooner.
If for instance, you create a word for a story and Libre flags it as a wrong spelling, you can then add it to the progs dictionary, is there a way to do the same for a synonym for the word you created?

Short answer: no, it is not possible.

Longer: no, you cannot do it from within LibreOffice. You have to understand the syntax of thesaurus files and add new words accordingly. A thesaurus consists of two files, both being plain-text with some markup, thus can be edited with any text editor. I can’t advise further because I don’t understand thesauruses.

Thank you for your answer to my question, your time an help is much appreciated.