Danger of Queen covering one's King (4)
I believe the answer is:
risk
'danger' is the definition.
(risk is a kind of danger)
'queen covering one's king' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'covering' means one lot of letters go next to another (on top of in down clue).
'one's' becomes 'is' (roman numeral).
'king' becomes 'k'.
'r'+'is'+'k'='RISK'
'of' acts as a link.
(Other definitions for risk that I've seen before include "Jeopardy" , "Element of uncertainty" , "Possibility of bad outcome" , "Take a chance" , "Gamble" .)