Digit, two or eight, originally (3)
I believe the answer is:
'digit' is the definition.
(digit on a foot)
'two or eight originally' is the wordplay.
'originally' indicates taking the first letters.
The first letters of 'two or eight' is 'TOE'.
(Other definitions for toe that I've seen before include "Feature of footwear" , "compliantly put on line" , "Digit on foot" , "Conform or obey; ... the line" , "Front of shoe" .)