Former Queen Mother supporting upper-class side at Lords (7)
I believe the answer is:
quondam
'former' is the definition.
(I know that former can be written as quondam)
'queen mother supporting upper-class side at lords' is the wordplay.
'queen' becomes 'qu' (abbreviation for queen).
'mother' becomes 'dam' (female parent of an animal).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'upper-class side at lords' becomes 'on' (I can't justify this - if you can you should believe this answer much more).
'dam' put after 'on' is 'ondam'.
'qu'+'ondam'='QUONDAM'
Can you help me to learn more?
(Other definitions for quondam that I've seen before include "Former (Latin) - man quod (anag)" , "Erstwhile" .)