(idiomatic) in first place in a contest

(transitive, idiomatic) to mislead, to try to make someone believe a lie. / (transitive, idiomatic) to encourage with the illusion of a romantic relationship.

plural of leading light

(idiomatic) An acclaimed expert, one of the foremost experts, a luminary. / (nautical, navigation) A light that helps to guide vessels into a port.

On a steam locomotive, an unpowered wheel located in front of the driving wheels.

On a steam locomotive, an axle connecting a coupled pair of unpowered wheels located in front of the driving wheels.

On a steam locomotive, a railroad truck to which wheel axles (and, hence, wheels) for one or more coupled pairs of unpowered wheels are attached through bearings, located in front of the driving wheels.

Of or pertaining to the leading edge of an airfoil / (by extension) leading, latest or most up-to-date

(aeronautics) The frontmost edge of a wing or other airfoil of an aircraft; sometimes contains slots or slats / (by extension) The foremost part of a trend etc; a vanguard

(linear algebra) A main diagonal.