Famous ostrich with head in ideal ground (8)
I believe the answer is:
historic
'famous' is the definition.
(I've seen this before)
'ostrich with head in ideal ground' is the wordplay.
'with' is a charade indicator (letters next to each other).
'head in' says to take the initial letters.
'ground' indicates anagramming the letters ('grind' the letters into a new form).
The initial letter of 'ideal' is 'i'.
'ostrich'+'i'='ostrichi'
'ostrichi' is an anagram of 'HISTORIC'.
(Other definitions for historic that I've seen before include "Of significance in the past" , "Epoch-making" , "Redolent of past glories" , "Significant" , "Pertaining to what is important in the past" .)