In a tomb weirdly harbouring one desire (8)
I believe the answer is:
ambition
'desire' is the definition.
(ambition is a kind of desire)
'in a tomb weirdly harbouring one' is the wordplay.
'weirdly' indicates an anagram.
'harbouring' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'in'+'a'+'tomb'='inatomb'
'inatomb' is an anagram of 'ambiton'.
'ambiton' enclosing 'i' is 'AMBITION'.
(Other definitions for ambition that I've seen before include "Desire to succeed in the world" , "Aspiration - goal" , "Strong desire for success" , "Aspiration, dream" , "Strong desire to achieve, fame or fortune" .)