Take in topless cab before brothers turn up (6)
I believe the answer is:
absorb
'take in' is the definition.
(synonyms)
'topless cab before brothers turn up' is the wordplay.
'topless' means to remove the first letter.
'before' says to put letters next to each other.
'brothers' becomes 'bros'.
'turn up' says the letters should be written backwards.
'bros' in reverse letter order is 'sorb'.
'cab' with its first letter removed is 'ab'.
'ab'+'sorb'='ABSORB'
(Other definitions for absorb that I've seen before include "Soak up - engross" , "Understand" , "Carved figure" , "Assimilate or soak up" , "Assimilate, ingest" .)