Thursday in March: a girl appears (6)
I believe the answer is:
martha
'girl appears' is the definition.
I can't tell whether this defines the answer.
'thursday in march a' is the wordplay.
'thursday' becomes 'th' ('Th' can be a synonym of 'thursday').
'in' indicates putting letters inside.
'march' becomes 'mar' ('Mar' can be a synonym of 'march').
'mar'+'a'='mara'
'th' inserted inside 'mara' is 'MARTHA'.
(Other definitions for martha that I've seen before include "Sister of Mary and Lazarus (New Testament)" , "George Washington's wife; at harm (anag.)" , "Girl's name; Washington's wife" , "Bible sister of Lazarus and Mary" , "Woman noted for work" .)