Horrid sailor admitted? It's feasible (6)
I believe the answer is:
viable
'it's feasible' is the definition.
(synonyms)
'horrid sailor admitted?' is the wordplay.
'horrid' becomes 'vile' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sailor' becomes 'ab' (abbreviation for able seaman).
'admitted?' indicates putting letters inside (inserted letters are admitted in).
'vile' enclosing 'ab' is 'VIABLE'.
Can you help me to learn more?
(Other definitions for viable that I've seen before include "Having a chance of success" , "Able to function, grow normally" , "Fumbled" , "Capable of independent life" , "reasonable hope of success" .)