The adjective funereal means like a funeral or mournful or gloomy. It usually doesn’t apply to things directly related to or involved with funerals. For example, planning for a funeral is not referred to as funereal planning, and music played at a funeral isn’t funereal music. Funeral serves as the adjective in these instances—e.g., funeral planning, and funeral music—and funereal is usually reserved for atmosphere, tones, and moods. The atmosphere in a sports stadium at the end of a blowout of the home team might be called funereal, for instance, as might the mood in a community in the days after a tragedy.
Funereal usually describes things that don’t actually relate to funerals, as in these cases:
Their cabaret-laced psychedelia may veer toward the funereal, but this trio from Baltimore is wholly enjoyable live. [New York Times]
There was an almost funereal atmosphere in the dressing room after the game. [Sydney Morning Herald]
Still, guests called the mood at Dior funereal, with black ribbons on the guests’ chairs and a solemn address. [Vancouver Sun]
For things that do have to do with funerals, funeral doubles as an adjective—for example:
A Park Forest woman who used somebody else’s credit card number to pay for pizza for a funeral gathering has been charged with identity theft. [Chicago Sun-Times]
The 36-year-old … is a victim of a callous price-cutting war enveloping the funeral industry. [Courier Mail]