House plant possibly under glass (7)
I believe the answer is:
coaster
'under glass' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'house plant' is the wordplay.
'house' becomes 'co' (I can't justify this - if you can you should give a lot more credence to this answer).
'plant' becomes 'aster' (aster is a kind of plant).
'co'+'aster'='COASTER'
'possibly' acts as a link.
Can you help me to learn more?
(Other definitions for coaster that I've seen before include "Mat to protect a table" , "Mat for decanter or glasses" , "... another one [VESSEL]" , "Tray; trader" , "Ship; (drinks) mat" .)