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