Hard ground that's by the fire (6)
I believe the answer is:
hearth
'the fire' is the definition.
(I've seen this before)
'hard ground that's by' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'ground' becomes 'earth' (synonyms).
'that's by' says to put letters next to each other.
'h'+'earth'='HEARTH'
(Other definitions for hearth that I've seen before include "Area around the fire" , "part of furnace" , "Part of fireplace symbolising home" , "a warm, welcoming place" , "Floor of a fireplace in the home" .)