Meghan's opening Spare for old lady (6)
I believe the answer is:
mother
'for old lady' is the definition.
(thesaurus)
'meghan's opening spare' is the wordplay.
'opening' indicates taking the first letters.
'spare' becomes 'other' (other can mean spare or alternative).
The first letter of 'meghan' is 'm'.
'm'+'other'='MOTHER'
(Other definitions for mother that I've seen before include "One who pours the tea?" , "Fuss over" , "Parent to her Tom, oddly" , "Female parent" , "She gave birth to her Tom" .)