Wavering of ambassador initially inept in post (10)
I believe the answer is:
hesitation
'wavering' is the definition.
(synonyms)
'ambassador initially inept in post' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'initially' indicates taking the first letters.
'in' means one lot of letters goes inside another.
'post' becomes 'station' (synonyms).
The initial letter of 'inept' is 'i'.
'i' going within 'station' is 'sitation'.
'he'+'sitation'='HESITATION'
'of' is the link.
(Other definitions for hesitation that I've seen before include "indecision" , "Reluctance" , "Pause" , "Wavering" .)