Vigilant prince consort ditches bishop (5)
I believe the answer is:
alert
'vigilant' is the definition.
(similar in meaning)
'prince consort ditches bishop' is the wordplay.
'prince consort' becomes 'Albert' (Prince Albert, husband of Queen Victoria).
'ditches' indicates named letters should be taken away.
'bishop' becomes 'B' (chess abbreviation).
'albert' with 'b' taken out is 'ALERT'.
(Other definitions for alert that I've seen before include "Danger warning" , "Lively" , "On one's toes" , "'Attentive, watchful (5)'" , "Watchful; warning" .)