Blue flag and Iris

Blue flag noun - A common iris of the eastern United States having blue or blue-violet flowers; root formerly used medicinally.

Iris and blue flag are semantically related. In some cases you can use "Iris" instead a noun phrase "Blue flag".

Iris noun - Muscular diaphragm that controls the size of the pupil which in turn controls the amount of light that enters the eye; it forms the colored portion of the eye.

Blue flag and iris are semantically related. Sometimes you can replace phrase "Blue flag" with "Iris", this terms are similar.