The term 'CLIMBS ABOARD' can be solved by two crossword solutions: HOPSON (6 letters) and ENTRAINS (8 letters). HOPSON is a verb meaning to board a vehicle, such as a train or bus, by hopping on. ENTRAINS is also a verb, meaning to board a train, usually in a group. Both words describe the action of getting on a vehicle, but HOPSON implies a single person boarding, while ENTRAINS implies multiple people boarding at once.