What is another word for like a rail?
Pronunciation: [lˈa͡ɪk ɐ ɹˈe͡ɪl] (IPA) 
"Like a rail" is a common idiom used to describe someone who is extremely thin and bony. There are various synonyms that can be used to convey a similar meaning. One term often used is "emaciated", which suggests extreme thinness and malnourishment. Another option is "skeletal", which emphasizes the appearance of the person's bones. "Gaunt" is also a suitable synonym, suggesting a haggard and scrawny appearance. "Skinny" and "thin" are less formal but still appropriate synonyms to use. Lastly, "wiry" can be used to describe someone who is thin, but also has a lean and muscular build.
