Maybe..these word mean same thing.
but I think some different between 심심하다 and 지루하다.
When we have nothing to do, we use 심심하다.
When we are boring, although we do something(like job, study, washing dish..etc)
We use 지루하다.
Example sentence in Korean.
할게 없어서 너무 심심해.
공부만 했더니 지루하다.
Verb match.
심심하다.
bored
지루하다.
boring, bored, dull, tedious, tiresome, wearisome