If you are looking for an idiom, your first port of call (after Google!) should be to click on the word "Reference" at the top of each page, then click on "Idioms". From there, you can look at them alphabetically, or do a search. If you had, you would have found this: On your high horse - Idiom Definition - UsingEnglish.com
Your other question is not about idioms so you should start a new thread about the conditional clause within the "Ask A Teacher" section of the forum.
Student or Learner