Expeditions. You aren't trying to say that on one expedition many explorers died. You are trying to say that over the course of many different expeditions, many explorers died. To do so, explorers and expeditions must agree.

I'm catching your drift. I'm tracking. I'm following. Gotcha. (Slang for I got you->Got you->Got ya->Gotcha)

Ditto is commonly used. Actually I typically hear it used as simply "ditto" to replace the entire sentence "Same to you."

They are usually used interchangeably in conversation. In reality, a syllabus will typically describe the requirements of a subject, while a curriculum covers the requirements of an entire course of study. For example a 7th grade science class could have an overall curriculum and an astronomy syllabus. I don't usually see anyone note this distinction however.

It depends on the context but they likely mean the same thing. Older is much more commonly used though. Elder is usually used in the forms "an elder," "an elderly person" (an old person), or "respect your elders" (give older people the respect they deserve). Hope this helps!

You drive me up a wall. (You're being very obnoxious/annoying) Stuck between a rock and a hard place. (Unable to get out of an impossible situation), also known as a Catch 22. Bang for your buck. (Purchasing power, the quality of a $ deal)