Like its cousin macaroni, spaghetti is made from semolina and water. Sometimes eggs are added. The name of this pasta comes from the Italian word for "strings" and in general spaghetti is in the form of long, thin strands that are round and solid. Spaghettini is very thin spaghetti (but thicker than vermicelli). Some spaghettislike fettuccine and linguineare flat rather than round. On the other hand, fusilli is a spiral shape, rather than being straight.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.