Occurring twice a week; occurring once every one-half a week(adjective)
Twice a week.(adverb)
A periodical published twice a week.(noun)
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Use "semi-weekly" in a sentence
"Who would have thought that online bill paying would mean we are far less frequently facing semi-weekly "discussuments" not a discussion but not quite an argument about who got the mail from the mailbox and where it was set down?"
"Mr. Katz is editor of the semi-weekly Oriental Economist Alert."
"This is a semi-weekly segment, at least that's how I'm aiming it, but this week's browsing proved to eventful."