Noun
infrakingdom (plural infrakingdoms)
(taxonomy) A taxonomic category sometimes inserted below subkingdom.
In some classification systems the additional rank branch (Latin: ramus) can be inserted between subkingdom and infrakingdom (e.g. Protostomia and Deuterostomia in the classification of Cavalier-Smith citation ). Source: Internet
Prefixes can be added so subkingdom and infrakingdom are the two ranks immediately below kingdom. Source: Internet