A number of fingers (5)
I believe the answer is:
frost
This might be a double definition.
'a number' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'of fingers' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for frost that I've seen before include "Rime" , "Frozen deposit" , "Icy deposit" , "Ice crystals forming a white deposit" , "Robert ---, US poet" .)