Glower when tense, harbouring a mild disease (9)
I believe the answer is:
taillight
'glower' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'tense harbouring a mild disease' is the wordplay.
'tense' becomes 'tight' (associated in meaning).
'harbouring' is an insertion indicator.
'mild disease' becomes 'ill' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'ill'='aill'
'tight' enclosing 'aill' is 'TAILLIGHT'.
'when' acts as a link.
Can you help me to learn more?
(Another definition for taillight that I've seen is " Illumination at rear of vehicle".)