a very stupid or foolish person
About the word:
Pillock (which has also on occasion been spelled pilloch, pillok, and pillick) is one of the hundreds of euphemisms for the male sexual organ in the English language. The Oxford English Dictionary records the earliest known use of the word in 1568, and for several hundred years this was apparently the main sense of the word. However, begining in the late 20th century pillock took on another meaning, which is that of an idiot or fool of some sort. Both of these uses are almost entirely confined to British English, and the word has little currency in the United States.