Nothing in Washington for one of seven small people (3)
I believe the answer is:
doc
'one of seven small people' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'nothing in washington' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' means one lot of letters goes inside another.
'washington' becomes 'dc' (Washington DC).
'o' placed within 'dc' is 'DOC'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for doc that I've seen before include "One of the seven dwarfs" , "Quack" , "Medical practitioner (abbr)" , "scaled-down version of GP" , "GP (colloq.)" .)