half-hourly

half-hour +‎ -ly

half-hourly (not comparable)

1. Once every half-hour, every 30 minutes.

   a half-hourly train service

   • 2019 October, “Lee Valley shuttle service launched”, in Modern Railways, page 18:

     A new half-hourly service between Stratford [Greater London] and Meridian Water was introduced on 9 September by Greater Anglia.

• semihourly

half-hourly (not comparable)

1. At intervals of a half-hour, every 30 minutes.

   Take this medicine half-hourly.

• twice-hourly
• semihourly