Get sick on second cruise (4)
I believe the answer is:
sail
'cruise' is the definition.
(I know that cruise can be written as sail)
'get sick on second' is the wordplay.
'get sick' becomes 'ail' (to ail is to become ill).
'on' means one lot of letters go next to another.
'second' becomes 's' (common abbreviation).
'ail' put after 's' is 'SAIL'.
(Other definitions for sail that I've seen before include "Spanker, say" , "Be 4 [SEABORNE]" , "Spanker or spinnaker, for example" , "project" , "Go by water" .)