keep a straight face

:  to retain in one's possession or power

:  to refrain from granting, giving, or allowing

:  to have in control

:  the means or provisions by which one is kept

:  one that keeps or protects: such as

:  fortress, castle

:  free from curves, bends, angles, or irregularities

:  generated by a point moving continuously in the same direction and expressed by a linear equation

:  lying along or holding to a direct or proper course or method

:  in a straight manner

:  straighten

:  something that is straight: such as

:  a straight line or arrangement

:  straightaway

:  the front part of the head that in humans extends from the forehead to the chin and includes the mouth, nose, cheeks, and eyes

:  the face as a means of identification :  countenance

:  presence, sight

:  to confront impudently

:  to line near the edge especially with a different material

:  to cover the front or surface of