"The study of word origins and derivatives helps students grasp an essential linguistic principle: English words have a discernible logic because their meanings are historically grounded. This knowledge, used in conjunction with word analysis skills, empowers them as learners." (Padak, N., Newton, E., Rasinski, T., & Newton R. N., 2008, p. 7)
Etymology is the study of the historical origins for the smallest linguistic units that carry meaning (morphemes). In English, this study often leads us to Greek and Latin origins. Using etymology to make meaning from the word "photograph" would lead to dividing the word into two units. The Greek "photo" meaning light and the Greek "graphos" meaning to write, record, or paint. Which leads to "photograph" meaning light picture, or a record of light. In contrast, knowing that adding an "s" to the end of the word "book" adds the meaning of more than one book, would not be etymology, but morphology.