Memoir Or Autobiography?

The other day I wrote about a review I'd read of Donald Rumsfield's new book. I called it a memoir, and one of my Followers wrote a comment regarding using the word memoir for a book of this type. She felt this is more of an autobiography. She's a memoir writer and teaches others to write memoirs, so I respect her opinion.

I wondered if I'd goofed and used the word memoir on my own. So I checked the book on Amazon, and the title is Known and Unknown and underneath that it says A Memoir. I breathed a sigh of relief because I don't like to make mistakes and I especially don't like to make them publicly.

I kept thinking about it, however, so this morning I went to Webster to define memoir and autobiography. The dictionary gave me this for memoir:

Definition of MEMOIR

1

: an official note or report : memorandum

2

a : a narrative composed from personal experienceb : autobiography —usually used in pluralc : biography

3

a : an account of something noteworthy : reportb plural : the record of the proceedings of a learned society

and the definition of autobiography is:

au·to·bi·og·ra·phy

 noun \ˌȯ-tə-bī-ˈä-grə-fē, -bē-\

: the biography of a person narrated by himself or herself

So it looks like an autobiography can also be termed a memoir. If you adhere to dictionary definitions, they might be used interchangeably.  My personal feeling is that an autobiography is  the complete story of a life. A memoir can be the same, or it can be just one slice of the pie.