Spine / สัน
Thai and English share the same concept of a spine. สัน means “spine,” for men and for books.
English speakers understand “spine” alone to mean the backbone. But in Thai, that is กระดูกสันหลัง—so it’s not a perfect match with English, but still easy to remember.
The spine of a book is สันหนังสือ (literally, “book spine”), correlating with English very closely.
Just remember that the spines (little sharp things) on porcupines and sea urchins are not the same word in Thai. That is a different concept with different words in each language.
Update February 4, 2008: Thanks to Rikker for pointing out in the comments that “ridge” is likely the best meaning for สัน. So go ahead and remember “spine” as a mnemonic for backbones and books; but to take it further, “ridge” is better for understanding.