Work out sequence (5)
I believe the answer is:
train
I believe this is a double definition.
'work out' is the first definition.
(I know that train is a more specific form of the action the work out)
'sequence' is the second definition.
(I've seen this before)
(Other definitions for train that I've seen before include "Trailing material on dress" , "Suite; give practice (in)" , "Railway engine" , "See 17" , "tutor" .)