half-open

From half- + open.

half-open (not comparable)

1. partially open; ajar
   • 1964 April, G. Freeman Allen, “The BRB shows traders the Liner train prototypes”, in Modern Railways, page 265:

     Between the fixed, full-height ends run flexible covers, carried on tubes running in guides, which can be locked in the closed, half-open or fully open positions; [...].

2. (mathematics) (referring to an interval on the real line) containing only one of its endpoints