tǐng​zhí

straighten

挺直 tǐng​zhí
straighten verb
to make straight or hold erect, especially one's back or body

Hearing the teacher come in, he immediately straightened his back.

upright verb
being in a vertical or straight position; erect

He sat very upright and looked very energetic.

Frequency

Movie subtitles
1.34 per million appears in 0% of films
Written text
1.88 per million

Sources

Definitions
CC-CEDICT