semiformal

Etymology

From semi- + formal.

adj

1. Somewhat formal.
   The HLA defines the rules of interoperability, a semiformal methodology for specifying simulation and federation object classes, and the interface specification that is a precise specification of the functional actions that a simulation may invoke. 2006, Stanislaw Raczynski, Modeling and Simulation: The Computer Science of Illusion, page 31
   When wearing the dragon robe on semiformal occasions, a single necklace was appropriate. Only the empress or empress dowager could wear a main necklace formed of Manchurian pearls, the other two being made of coral. 2007, Valery Garrett, Chinese Dress: From the Qing Dynasty to the Present, page 40
2. (Canada, US, specifically) Of clothing: having a level of formality between that of informal and formal wear.
   Suits have largely replaced guayabera shirts as business and semiformal wear for middle and upper-class Panamanian men, made practical by the widespread use of air-conditioning in the cities. 2005, Williams Friar, Panama, 1st edition, Emeryville, C.A.: Moon Handbooks, →ISSN, →OCLC, page 528
3. (Canada, US, specifically) Of an event: having a semiformal dress code.
   The skirt was way too short, at least shorter than she preferred. It left exposed a good eight inches between her knee and thigh. But what choice did she really have? Casual cropped pants were hardly appropriate attire for a semiformal event. 2006, Marcia King-Gamble, Designed for You, New York, N.Y.: Kimani Press, page 32

noun

1. (Canada, US) A social event in which one is expected to dress in semiformal wear.
   Bright-colored flyers decorated battered lockers, telling everyone to join the debate team, try out for the school play, and not to miss the fall semiformal this Friday. I wondered what a "semiformal" consisted of at a public school, not that I'd bothered to ask anyone. 2010, Amanda Hocking, Switched (Trylle Trilogy; 3), New York, N.Y.: St. Martin's Griffin, published 2012, page 9