bus / busses / buses
The plural of the vehicle, and the kiss.
The plural of the vehicle is buses. Busses is the older plural of bus, and it is also the present-tense verb and the plural noun for kisses: she busses him. For the vehicle, write buses.
Examples
UseTwo buses were late.
UseShe busses him on the cheek.
AvoidTwo busses were late. (If you mean the vehicles.)