Girls one notices being absent (6)
I believe the answer is:
misses
'girls' is the definition.
('miss' can be a synonym of 'girl')
'one notices being absent' is the wordplay.
'one' becomes 'mis' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'notices' becomes 'senses'.
'being' becomes 'ens' (I've seen this in other clues).
'absent' indicates named letters should be taken away.
'senses' with 'ens' taken away is 'ses'.
'mis'+'ses'='MISSES'
Can you help me to learn more?
(Other definitions for misses that I've seen before include "Fails to meet" , "young women" , "Failures to hit" , "Young ladies; avoids" , "Unsuccessful attempts" .)