Wiktionary
smooth muscle
n. (context muscle English) involuntary muscle which is found within the intestines, throat, uterus, and blood vessel walls.
WordNet
smooth muscle
n. a muscle that contracts without conscious control and found in walls of internal organs such as stomach and intestine and bladder and blood vessels (excluding the heart) [syn: involuntary muscle]
muscle tissue that does not appear striated under the microscope; has the form of thin layers or sheets