(military, nautical) Abbreviation of rear admiral.

(medicine, dermatology) Initialism of alopecia universalis. / (astronomy) Initialism of astronomical unit. / Initialism of angstrom unit. / (fandom slang) Initialism of alternate universe.

(nautical) A rope attaching to the clew (lower corner) of a sail, used to furl it.

(intransitive) To move in a direction opposite to that which one is facing, keeping one's attention on the thing in front being avoided.