Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
1530s, dialectal variant of Middle English pillicock (see cock (n.1)). Meaning "stupid person" is attested by 1967.
Wiktionary
n. (context British mildly pejorative slang English) a stupid or annoying person; simpleton; fool.
WordNet
n. a person who is not very bright; "The economy, stupid!" [syn: stupid, stupid person, dullard, dolt, pudding head, pudden-head, poor fish]
Wikipedia
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Usage examples of "pillock".
Like a pillock I drove obediently through Lavenham, wondering why the hell I was bothering.
The useless pillock in one of his usual drunken flaps, so what else was new?
This is something I have to do with Dobbs, and believe me Calvin, if I could choose you instead of that dozy pillock I would.
Sometimes, it is true, I find it hard to keep quiet when I must listen to the boasting of tumblers and other pillocks who are not fit to serve you.