Definition from Wiktionary, the free dictionary
subfenestral (not comparable)
- Of or pertaining to the underside of or space beneath a fenestra or window.
- The wall was clean, save for a patch of subfenestral graffiti.
- 1829, "Dr. George Shaw," in Personal and Literary Memorials, by Henry Digby Beste
- We even went down into the cellars, where was a vast vault filled with coal. "This puts to shame the subfenestral carbonaria of your alma mater." Every university-man knows how the coal-porter brings his sack on his shoulder, and empties the load into the hollowed-out window-seat; Forsan et haec olim meminisse juvabit.
- 1996, "In a Different Place: Feminist Aesthetics and the Picture Book", by Anne Lundin, in Ways of Knowing Kay E. Vandergrift, ed. 
- Under the Window’s subfenestral world is full of openings as well as suggestive of the ground, the underground of life.
- 2002, "Archaeopterygidae", by Andrzej Elzanowski, in Mesozoic Birds, Luis M. Chiappe & Lawrence M. Witmer edd.
- The maxilla has a slender nasal process and a long subfenestral part. [...] Wellnhofer (1974) and Witmer (1997) reconstructed a fenestrate "ascending ramus" of the maxilla, as found in nonavian theropods.