Part with a group at Heathrow Central (5)
I believe the answer is:
tenth
'part' is the definition.
(I've seen this before)
'a group at heathrow central' is the wordplay.
'a group' becomes 'ten' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at' means one lot of letters go next to another.
'central' says to take the centre.
The centre of 'heathrow' is 'th'.
'ten'+'th'='TENTH'
'with' is the link.
Can you help me to learn more?
(Other definitions for tenth that I've seen before include "One behind ninth" , "after nine" , "Decimal part?" , "Tithe proportion" , "Ordinal number" .)