quarter-hour

[kwawr-ter-ouuh r, -ou-er] /ˈkwɔr tərˈaʊər, -ˈaʊ ər/
noun
1.
a period of 15 minutes.
2.
a point 15 minutes after or before the hour.
Origin
1880-85
British Dictionary definitions for quarter-hour

quarter-hour

noun
1.
a period of 15 minutes
2.
any of the points on the face of a timepiece that mark 15 minutes before or after the hour, and sometimes 30 minutes after
Derived Forms
quarter-hourly, adverb, adjective