[adjective] [not gradable] - impossible to take apart or bring to an end; existing for a very long timeGoing through the tragedy together forged an indissoluble bond of friendship between them which would last until they died.The links between the two nations are indissoluble.
INDISSOLUBLE
Meaning of INDISSOLUBLE in English
Cambridge English vocab. Кембриджский английский словарь. 2012