Place in one's diary to have nice new entry in place (6)
I believe the answer is:
pencil
'entry in place' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'place in one's diary to have nice new' is the wordplay.
'place in one's diary' becomes 'pl' (I am not sure about this - if you are sure you should believe this answer much more).
'to have' means one lot of letters goes inside another.
'new' indicates an anagram.
'nice' anagrammed gives 'enci'.
'pl' enclosing 'enci' is 'PENCIL'.
Can you help me to learn more?
(Other definitions for pencil that I've seen before include "implement in case?" , "American bureaucrat -- purple niches (anag)" , "A writing stick" , "__-sharpener" , "Drawer with graphite in" .)