Careless manicure, losing one of digits (7)
I believe the answer is:
numeric
'of digits' is the definition.
(relating to digits or numbers)
'careless manicure losing one' is the wordplay.
'careless' is an anagram indicator.
'losing' indicates named letters should be taken away.
'one' becomes 'a' (a thing is one thing).
'manicure' with 'a' taken away is 'mnicure'.
'mnicure' anagrammed gives 'NUMERIC'.
(Other definitions for numeric that I've seen before include "Expressed in numbers" , "Expressed using digits" , "Consisting of numbers" , "Employing figures" , "Relating to numbers" .)