Passenger ships (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">passenger ships</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for liners that I've seen before include "These go inside" , "craft?" , "Large ocean-going ships" , "Large commercial ships" , "cruise ships" .)