The Collaborative International Dictionary
To straighten one's face
Straighten \Straight"en\, v. t. [imp. & p. p. Straighted; p. pr. & vb. n. Straighting.]
To make straight; to reduce from a crooked to a straight form.
-
To make right or correct; to reduce to order; as, to straighten one's affairs; to straighten an account.
To straighten one's face, to cease laughing or smiling, etc., and compose one's features.