What does "rectus" mean?

Any of several straight muscles in various parts of the body, as of the abdomen, thigh, eye etc.; Ellipsis of rectus abdominis.

Rectus

Common synonyms include: erect, extraocular straight muscle, eye straight muscle, linear, linear muscle, longitudinal muscle.

/ˈɹɛk.təs/ noun

noun ·Rare ·Advanced level

Noun

1
Any of several straight muscles in various parts of the body, as of the abdomen, thigh, eye etc.; Ellipsis of rectus abdominis. abbreviation, alt-of, ellipsis
2
any of various straight muscles wordnet
3
Any of several straight muscles in various parts of the body, as of the abdomen, thigh, eye etc.; Any of a number of muscles controlling the movement of the eyeball.

"The quadriceps is made up of four muscles: the rectus femoris, the vastus medialis, the vastus intermedius and the vastus lateralis."

Borrowed from Latin rēctus (“straight, upright”), clipping of mūsculus rēctus (“straight muscle”).