Iris may have one, so have you and I (9)
I believe the answer is:
diaphragm
'iris' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for diaphragm that I've seen before include "Partitioning membrane" , "Partition between thorax and abdomen" , "It separates the thorax from the abdomen" , "Flexible membrane" , "Thin dividing membrane" .)