Trembling, from mum: 'I'm engaged?' (9)
I believe the answer is:
shivering
'trembling' is the definition.
(shivering is a kind of trembling)
'mum i'm engaged?' is the wordplay.
'mum' becomes 'sh' (both are used to tell someone to be quiet).
'i'm engaged?' becomes 'ivering' (I have an engagement ring).
'sh'+'ivering'='SHIVERING'
'from' is the link.
(Other definitions for shivering that I've seen before include "trembling?" , "excited" , "Shaking (with the cold)" , "Evidently cold" .)