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An innocuous name for an erection (or 'semi hardon').

The phrase originated from the James Blunt song 'Wisemen'. In which, 'Those three Wise Men' are cited as having 'a semi by the sea' (of course, in reality, they are referring to a semi-detached house).

The word has become increasingly used among British and some American internet forums.
"Oh my god...these photos of Keeley Hazel are giving me a full on semi by the sea lolololol"
by JamieFKA May 21, 2008
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