Also found in: Thesaurus, Medical, Encyclopedia.


1. Platelike.
a. Relating to or being a kind of fish scale that is a toothlike plate with a protruding spine, characteristic of sharks, skates, and rays.
b. Having placoid scales.

[Greek plax, plak-, flat stone, plate; see plāk- in Indo-European roots + -oid.]


1. (Biology) platelike or flattened
2. (Zoology) (of the scales of sharks and other elasmobranchs) toothlike; composed of dentine with an enamel tip and basal pulp cavity
[C19: from Greek plac-, plax flat]


(ˈplæk ɔɪd)

platelike, as the scales or dermal investments of sharks.
[1835–45; < Greek plak- (s. of pláx) something flat, tablet]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Adj.1.placoid - as the hard flattened scales of e.g. sharks
planar, two-dimensional - involving two dimensions
References in periodicals archive ?
Male antennae possess a number of olfactory multiporous trichoid sensilla which could function for perception of mating-related volatile cues, whereas female antennae are characterized by more multiporous placoid sensillia suggesting greater sensitivity to host-related volatile cues (Onagbola et al.
Syphilitic chorioretinitis presents as a vitritis associated with bilateral, large, solitary, placoid, pale yellow subretinal lesions with central fading and stippled retinal pigment epithelial (RPE) hyperpigmentation.
Efficacy of cyclosporine A in the treatment of acute posterior multifocal placoid pigment epitheliopathy.
Inflammatory etiologies include uveitis-glaucoma-hyphema syndrome, sympathetic ophthalmia, sarcoidosis, pars planitis, multiple sclerosis, rheumatoid arthritis, birdshot chorioretinopathy, Behcet disease, Vogt-Koyanagi-Harada disease, sterile endophthalmitis, multifocal choroiditis, and acute posterior multifocal placoid pigment epitheliopathy.