underline
US /ˌʌn.dɚˈlaɪn/
UK /ˌʌn.dɚˈlaɪn/

1.
下線を引く
a line drawn under a word or phrase, especially for emphasis.
:
•
subheadings have an underline in blue
2.
下線を引く
the line of the lower part of an animal's body.
:
•
she has a white tail and underline