The cake was burnt to a cinder (=completely burnt).cindercin‧der /ˈsɪndə $ -ər/ noun [countable usually plural] 
a cold hearth full of cinders The cake was burnt to a cinder (=completely burnt).
WORD ORIGINcinder
Origin:
Old English sinder; influenced by French cendre ‘ashes’EXAMPLES FROM OTHER DICTIONARIES
- Burning cinders fell onto the roof.
- A cooking pot hung on a tripod though the logs beneath were now blackened cinders.
- His chill was replaced by hot cinders deep in his heart.
- If the foundation is made of cinder blocks, they need to be set in a bed of mortar on the concrete.
- It uses the ground's grass areas and cinder track for training.
- Pearce, wanting to take a quick throw-in, grabbed the ball and pushed him on the cinder track surrounding the pitch.
- She'd even felt quite calm, only thinking that in the oven his dinner would be in cinders now.
- The room is maybe six feet square, with cinder block walls.
- Three small houses, made of painted cinder block and aluminum, faced the hotel from across the street.
COLLOCATIONS FROM THE ENTRY The cake was burnt to a cinder (=completely burnt).COLLOCATIONS FROM THE CORPUSNOUN
a very small piece of burnt wood, coal etc: The cake was burnt to a cinder (=completely burnt).· They passed a Baptist church set on cinder blocks.· The room is maybe six feet square, with cinder block walls.· Three small houses, made of painted cinder block and aluminum, faced the hotel from across the street.· His bookshelves were plywood and cinder blocks.· If the foundation is made of cinder blocks, they need to be set in a bed of mortar on the concrete.· In Colonia Anapra, homes are made from plywood sheets, wooden pallets, unpainted cinder blocks and cardboard.
a cold hearth full of cinders The cake was burnt to a cinder (=completely burnt).