Small cube? (5)
'small cube?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eight that I've seen before include "Perfect cube" , "Chaps having row" , "Cardinal number" , "Number (with pieces?)" , "Number in octet" .)
(Other definitions for one that I've seen before include "Figure" , "Lowest cardinal number" , "If upper-class, perhaps I" , "both halves" , "This is singular" .)