< /ˈæb əˌsaɪ, -ˌkaɪ, əˈbæk aɪ/.

- a device for making arithmetic calculations, consisting of a frame set with rods on which balls or beads are moved.
- Architecture. a slab forming the top of the capital of a column.

noun plural -ci (-ˌsaɪ) or -cuses

- a counting device that consists of a frame holding rods on which a specific number of beads are free to move. Each rod designates a given denomination, such as units, tens, hundreds, etc, in the decimal system, and each bead represents a digit or a specific number of digits
- architect the flat upper part of the capital of a column

late 14c., “sand table for drawing, calculating, etc.,” from Latin abacus, from Greek abax (genitive abakos) “counting table,” from Hebrew abaq “dust,” from root a-b-q “to fly off.” Originally a drawing board covered with dust or sand that could be written on to do mathematical equations. Specific reference to a counting frame is 17c. or later.