cock-up noun 3cock up verb 1forms 4 noun3 •(slang, vulgar) A mistake.And I'm sorry for all the cock-ups, my cabinet are absolute crap. We'll have to do better next year. — 2003 •(UK, no longer used) A superior letter; a lower-case letter placed above the baseline and made smaller than ordinary script; traditionally used in abbreviations.The first word of every section or chapter is generally put in small capitals, after a small neat cock-up letter. — 1824 •(Scotland, no longer used) A roll or twist of hair worn at the nape of the neck; a bun. cock up verb1 •(slang, vulgar) To ruin (something) unintentionally; to fuck up, mess up, or screw up.It was cocking her up with gimcrack notions about ladies till she'd be ashamed to look at her own hands after she had done a day's work with them. — 1876 formscocked up · cocking up · cocks up · cock-ups