Noun
(music) The lower part of a tetrachord in Ancient Greek music, consisting of a composite interval (two successive intervals) that is less than the remaining (incomposite) interval.
Condensation, density.
(biology) A nonrandom pattern of repeated elements, which are found more frequently in the 3′ untranslated regions of genes than in other regions of the human genome. Although it is unclear how pyknons might have arisen, it is possible that they may be involved in a new form of gene regulation.
Source: en.wiktionary.org