Greatest head of state out of bed about to meet me (7)
I believe the answer is:
supreme
'greatest' is the definition.
(I've seen this before)
'head of state out of bed about to meet me' is the wordplay.
'head of' indicates taking the first letters.
'out of bed' becomes 'up' (synonyms).
'about' becomes 're' ('re' means regarding or about).
'to meet' says to put letters next to each other.
The initial letter of 'state' is 's'.
's'+'up'+'re'+'me'='SUPREME'
(Other definitions for supreme that I've seen before include "over the top" , "Paramount" , "Unrivalled" , "God" , "topmost level" .)