Inquisitive dog, faithful, with no lead (7)
I believe the answer is:
curious
'inquisitive' is the definition.
(similar in meaning)
'dog faithful with no lead' is the wordplay.
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'faithful' becomes 'pious'.
'with no lead' means to remove the first letter (the letter which leads the word is removed).
'pious' with its initial letter removed is 'ious'.
'cur'+'ious'='CURIOUS'
(Other definitions for curious that I've seen before include "Eager to know; strange" , "Strange - inquisitive" , "Eager to learn something" , "Odd or eager to know" , "with a great deal of interest!" .)