Cross as a beheaded buccaneer? (5)
'cross' is the definition.
(I've seen this before)
'a beheaded buccaneer?' is the wordplay.
'a beheaded' means to remove the first letter (the head of the word is removed).
'buccaneer?' becomes 'pirate' (synonyms).
'pirate' with its first letter taken away is 'IRATE'.
'as' acts as a link.
(Other definitions for irate that I've seen before include "Cross, irritated", "Spitting feathers", "Extremely angry", "Angry - furious", "become irritated".)