[wongarsu]

The term memoization likely precedes the word caching (as related to computing, obviously weapon caches are far older). Memoization was coined in 1968. CPU caches only came about in the 80s as registers became significantly faster than main memory.

As wikipedia outlines, the r was dropped because of the memo. It's derived from the latin word memorandum that does contain the r, just like memory, but apparently it was more meant as an analogy to written memos.