abreast of
Etymology
Old EnglishMiddle EnglishModern English
Abreast comes from the prefix a- (meaning 'on' or 'in') and breast, referring to the front of the chest. The literal image is of two people standing chest to chest, so close that their breasts are level. From this physical image the phrase developed the meaning of being side by side at the same height, first used for people and later extended to vehicles and objects.