The snuff or burnt wick of a candle.

1

1552.  Huloet, Snuffer of a candle or candlesnuffe.

2

1683.  Chalkhill, Thealma & Cl., 102. Her eyes like Candle-snuffs by age sink quite Into their Sockets.

3

1880.  Syd. Soc. Lex., Candle snuff … has been recommended for the cure of ague.

4