While a simile states that one thing is like another, a metaphor asserts that one thing is the other, or is a substitute for the other thing. A metaphor asserts a correlation or resemblance between two things that are otherwise unrelated.
ASL emerged as a language in the American School for the Deaf (ASD), founded in 1817. This school brought together Old French Sign Language, various village sign languages, and home sign systems; ASL was created in this situation of language contact. ASL was influenced by its forerunners but distinct from all of them.
First attested in a memo by US Representative (Texas) Maury Maverick dated March 30, 1944, banning gobbledygook language.