In astronomical contexts the headword - which otherwise means beams or planks - denotes a kind of comet, so called because of its shape. See e.g. Arrian, Fragmenta de rebus physicis 6.30 oi( komh=tai a)ste/res kai\ lampa/des kai\ pwgwni/ai kai\ pi/qoi kai\ doki/des, kaq’ o(moio/thta e(/kasta i)de/as th=s e)pwnumi/as laxo/nta; "the comets, the meteors, the 'bearded stars', the jar-shaped and the beam-shaped stars, which got their names according to an analogy to their shapes". Same explanation in Basil, In sanctam Christi generationem 31.1472.25 Migne; and cf. also Aristotle, De mundo 392b4; Eusebius, Demonstratio evangelica 9.1.14; Anna Comnena, Alexias 12.4.1. See also kappa 1996.
The noun doki/s is also used in mathematical contexts, as one of the several names given to different types of solid numbers (see LSJ at web address 1; Hesychius delta2120).