Passenger ship has a slender look (6)
I believe the answer is:
linear
'passenger ship has a slender look' is the definition.
I can't judge whether this defines the answer.
'passenger ship has a' is the wordplay.
'passenger ship' becomes 'liner' (eg a cruise liner).
'has' is an insertion indicator.
'liner' enclosing 'a' is 'LINEAR'.
Can you help me to learn more?
(Other definitions for linear that I've seen before include "In a straight line" , "-- Motor; -- equation" , "One-dimensional" , "Long and narrow, of one dimension" , "Measured lengthwise" .)