Wiktionary
wet fly
n. (context fishing English) A lure for fly fishing designed to be fished beneath the surface of the water.
WordNet
wet fly
n. fisherman's fly that floats under the surface of the water [ant: dry fly]
Usage examples of "wet fly".
He had achieved a good deal of purely theoretical knowledge of wet fly fishing by intensive study during the week, though not so much as might have been the case if his mind had not been occupied with his young woman.
Dick chose a colorful, wet fly from Lindley's collection, and cast upstream with care, but little finesse was needed: the stream was swarming with trout.