Definition of fenestella
1
plural -s
a
: a niche like a window in the south wall of the sanctuary near the altar (as of a Roman Catholic church) containing the piscina and often also the credence
b
: a small window or opening like a window (as in an altar front for allowing relics within to be seen)
2
capitalized
[New Latin, from Latin, small window]
: a genus (the type of the family Fenestellidae) of Paleozoic bryozoans whose colonies form lacy fronds — compare lace bryozoan 
