noun
market day
Refers to a fixed day when a regular market is held, often in a local or traditional context.
この町では毎月五日が市日です。
In this town, the 5th of every month is market day.
Compound of 市 (market) and 日 (day). The reading いちび is a straightforward combination of the on'yomi of 市 and the kun'yomi of 日.