Entire tungsten pit (5)
I believe the answer is:
whole
'entire' is the definition.
(similar in meaning)
'tungsten pit' is the wordplay.
'tungsten' becomes 'W' (W is the chemical symbol for tungsten).
'pit' becomes 'hole' (a pit is a hole).
'w'+'hole'='WHOLE'
(Other definitions for whole that I've seen before include "All the components" , "Integral" , "undamaged" , "Total" , "Complete, containing all the parts" .)