I was 'secure in the belief/knowledge' that I had done all I could. [=I felt confident because I believed/knew that I had done all I could]
They are 'financially secure'. [=they have enough money to live on; they do not have to worry about money]
You can access your bank account online using a 'secure' [='secret'] password.
(..) for returning, Potter. What is it you need? Time, Professor. As much as you can get me. Do what you have to do. I'll secure the castle. Potter... It's good to see you. It's good to see you too, Professor. Hold the fort, Neville. Harry! (..)2011 Harry Potter and the Deathly Hallows: Part 2