halfhourly

[haf-ouuh r-lee, -ou-er-, hahf-]

adjective

half-hour(def 3).
occurring every half-hour: a halfhourly interruption.

adverb

at half-hour intervals: The bell rang halfhourly.

Origin of halfhourly

First recorded in 1800–10; half + hourly

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018