Tip: on board ship, they help one look down on others (6)
I believe the answer is:
stilts
'they help one look down on others' is the definition.
(stilts let somebody stand taller than others)
'tip on board ship' is the wordplay.
'tip' becomes 'tilt' (synonyms).
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'tilt' inserted inside 'ss' is 'STILTS'.
(Other definitions for stilts that I've seen before include "Poles used for walking high above the ground" , "Long sticks for elevated walking" , "Sticks to help you walk tall" , "Walking poles; birds" , "Sticks to wall on" .)