The headword is neuter plural of the adjective di/krotos, the primary meaning of which is "double-beating". It is employed with reference to the human pulse in all of Galen's treatises on this matter, and also in Byzantine medical literature. However, the connection with oared ships is already evident in Euripides, Iphigenia in Tauris 408, and in Xenophon, Hellenica 2.1.28 it specifically means one with two banks of oars (web address 1); see also e.g. Duris FGrH 76 F66, who gives ploi=on di/kroton as a definition of the word samai/nh (cf. sigma 77; see also Hesychius eta507 h(mioli/a: h( di/krotos nau=s. As a substantive, to\ di/kroton (e.g. Polybius 5.62.3) is used especially in imperial prose: Plutarch, Lucullus 2.4; Appian, Mithridatica 17. Appian also (Illyrica 7) identifies the di/krota with the Roman naves Liburnicae, as [Lucian], Amores 6 tw=n dikro/twn, oi(=s ma/lista xra/sqai *liburnoi\ dokou=sin ("the dikrota, mostly used by the Liburnoi, as it seems". Feminine in Appian, Mithridatica 99; Greek Anthology 7.640.
[1] i.e. ships with two banks of oars. For this gloss see delta 1016. The adjective dih/rhs, meaning "double", as a substantive usually indicates a ship: cf. Pollux 1.82. *di/kroton is commonly referred to as a synonym of dih/rhs; see Arrian, Anabasis 6.5.2; Strabo 16.4.23 di/krota kai\ trih/reis kai\ fash/lous; Hesychius delta1759 dih/rhs nau=s: h(\n kai\ di/kroton kalou=sin, "a bireme ship, which they also call dikroton". For an association with the trireme see [Aelius Aristides], Rhodian Speech, p.539 Jebb, 27 trih/reis d' [...] u(pa/rxein i)dei=n dikro/tous kai\ trikro/tous ("one could see that there were triremes with two or three banks").
[2] Here begins a quotation from Cassius Dio 75.11.3 (not Adler's '74'), describing the three-year siege of Byzantium by the Roman army of the emperor Septimius Severus. The Suda has slightly modified the text we know from Johannes Xiphilinus’ epitome, which reads kai\ ploi=a de\ toi=s *buzanti/ois pentako/sia, ta\ me\n plei=sta (v. l. to\ me\n plei=ston) monh/rh, e)/sti d' oi(=a kai\ di/krota, kateskeu/asto e)mbo/lous e)/xonta: kai/ tina au)tw=n e(kate/rwqen, kai\ e)k th=s pru/mnhs kai\ e)k th=s prw/|ras, phdali/ois h)/skhto kai\ kubernh/tas nau/tas te diplou=s ei)=xen, o(/pws au)toi\ mh\ a)nastrefo/menoi kai\ e)piple/wsi kai\ a)naxwrw=si, kai\ tou\s e)nanti/ous kai\ e)n tw=| pro/splw| kai\ e)n tw=| a)po/plw| sfw=n sfa/llwsi. "The Byzantines had five hundred ships, equipped mostly with only one bank of oars, in some instances with two banks. Some of them were furnished with rudders on either side -- both at the prow and at the stern -– and had a double number of helmsmen, so that etc."
[3] The Suda has kateskeua/santo, i.e. third person plural aorist, instead of Dio's third person singular pluperfect kateskeu/asto; and the subsequent h)/skhto has been modified into a plural, h)/skhnto. One might expect a regular connection of the neutral di/krota with a singular verb, but this rule is typical of Attic and not constantly respected in the Koine. Moreover, Attic prose itself admits exceptions to the so-called schema Atticum when the emphasis is shifted on the plurality of inanimate objects: see e.g. Xenophon, Anabasis 1.8.20 ta\ a)/rmata e)fe/ronto ta\ me\n di' au)tw=n tw=n polemi/wn, ta\ de\ kai\ dia\ tw=n *(ellh/nwn, "the chariots were moved partly by the enemies themselves, partly also by the Greeks" (web address 2).