semi /ˈsɛmi/noun 7adverb 1forms 1 noun7 •(US, Australia) A semi-trailer; a tractor-trailer; an eighteen-wheeler; an artic.I was hungry an' freezin' an' done caught a chill / When the lights of a big semi topped the hill — 1967 •(UK, informal) A semi-detached house.I′m selling two side-by-side semis that are currently under construction, a waterfront apartment and a house in Rose Bay. — 2008 •(informal) A semifinal. •(slang) A partial erection of the penis.The twink got a semi just from that look. — 2010 •(slang) A semiautomatic firearm.See these niggas through the reticle sight up on my semi […] For niggas plottin', I might blow it at your fitted Get your bitch-ass slimed out, it ain't no kiddin' Ain't no kiddin', got that semi — 2023 •(slang) Semiconductor companies or positions in the stock market. •(informal) An intermediate in the production of end-use goods. adverb1 •(informal) Somewhat; to some extent.'Is that a serious question?' he asked. Ralph shrugged with his face, jutting out his bottom lip. 'Well ... semi,' he said. — 2013 formssemis