We don't have synonyms for hostrock yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are host rock, hot rock and rostock.
(n) :
Alternative form of host rock. [(geology) The background mineral material in which the object of study (crystals, fossils, specific minerals, groundwater, etc.) is embedded or through which it travels.]
(n) :
Alternative form of host rock. [(geology) The background mineral material in which the object of study (crystals, fossils, specific minerals, groundwater, etc.) is embedded or through which it travels.]