We don't have synonyms for pronephron yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are pronephros, pronephroi and pronephric.
(n) :
(biology) The first part of the urogenital system to be differentiated in a vertebrate embryo, which functions as a simple excretory organ in simpler forms, serves as a provisional kidney in some fish and amphibians, and only appears as a temporary embryonic structure in reptiles, birds, and mammals.
(n) :
(biology) The first part of the urogenital system to be differentiated in a vertebrate embryo, which functions as a simple excretory organ in simpler forms, serves as a provisional kidney in some fish and amphibians, and only appears as a temporary embryonic structure in reptiles, birds, and mammals.