Learn English – the difference between “probably” and “possibly”?

"Hence" means "from here". "Get thee hence!" is old English for "get out of here". "Henceforwards" is "from this time on".

"Thus" means "in this way". In older English, you might say "he opened the door thus", while demonstrating the action.

In logical senses, you can use them in similar contexts. "If x is true, then y is true. X is true. Hence, y is also true." "If x is true, then y is true. I have proved x is true. Thus, I have proved y to be true also."

Think of them as "based on this fact" and "in this way" and you can't go far wrong.

If something is probably true, then it may or may not actually be true.

Something is ostensibly true if someone has told you that it is supposed to be the case.