Is joking about the safety device (8)
I believe the answer is:
banister
'safety device' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'is joking about' is the wordplay.
'joking' becomes 'banter' (I've seen this in another clue).
'about' is an insertion indicator.
'is' inserted into 'banter' is 'BANISTER'.
'the' is the link.
Can you help me to learn more?
(Other definitions for banister that I've seen before include "Upright supporting handrail of stairs" , "Stair-rail" , "Stair handrail and supports" , "Staircase railing" , "support at hand on flight" .)