寝棺 is read as ねかん (nekan) and means coffin.
ねかん
nekan
ねすがた
one's figure during sleep
ねげしょう
cosmetics put on before going to bed
しんにつく
to go to bed
せっかん
sarcophagus
かん
coffin
しんだい
bed
ねまき
nightclothes
しん
sleep
しんしつ
bedroom
ねる
to ferment (of soy sauce, miso, etc.)
ねどこ
ねがえり
betrayal