[n] condition in which the cells of one tissue can survive in the presence of cells of another tissue; "a successful graft or translplant requires a high degree of histocompatibility"
HISTOCOMPATIBILITY is a 18 letter word that starts with H.
The ability of a tissue being transplanted from a donor to be accepted by and to function in the recipient (that is, without being attacked by the recipient's immune system). The chances of histocompatibility are much greater if the donor and recipient have the same or similar genotypes of histocompatibility antigens.
WordNet Dictionary