Merriam-Webster's Collegiate® Dictionary, 11th Edition
CASUAL
I. adjective see: case
Date: 14th century
subject to, resulting from, or occurring by chance ,
2. occurring without regularity ; occasional , employed for irregular periods , met with on occasion and known only superficially ,
3. a. feeling or showing little concern ; nonchalant , lacking a high degree of interest or devotion , done without serious intent or commitment , b. informal , natural , designed for informal use , see: accidental casually adverb casualness noun
II. noun
Date: circa 1852
a casual or migratory worker, an officer or enlisted person awaiting assignment or transportation to a unit