To grow worse in function or condition.

Support for people who are in the last months or years of their life. It should help you to live as well as possible until you die, and to die with dignity. (NHS Choices)
or
Care for people who are likely to die within 12 months, people with advanced, progressive, incurable conditions and people with life-threatening acute conditions. It also covers support for their families and carers. (NICE 2011)

An approach that improves the quality of life of patients and their families facing the problem associated with life-threatening illness, through the prevention and relief of suffering by means of early identification and impeccable assessment and treatment of pain and other problems, physical, psychosocial and spiritual.

The provision of the necessary services for those living with or affected by cancer (incurable illness) to meet their informational, emotional, spiritual, social, or physical needs during their diagnostic, treatment, or follow-up phases encompassing issues of health promotion and prevention, survivorship, palliation, and bereavement. (Curr Opin Oncol. 2014 Jul;26(4):372-9)
or
Treatment given to prevent, control, or relieve complications and side effects and to improve the patient's comfort and quality of life.