Side by side, with breasts in a line: as, “the riders rode abreast,” Dryden.
Nautical: Lying or moving side by side, with stems equally advanced. When used to indicate the situation of a vessel in regard to another object, opposite; over against; lying so that the object is on a line with the beam: in this sense with of.
Figuratively, up to the same pitch or level: used with of or with: as, to keep abreast of the times in science, etc. At the same time; simultaneously.