Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch

Smile because they are a mil between the first word and the last word hhhh

Floccinaucinihilipilification is the longest 'normal' word. It has 29 letters. I think it is pronounced more like flocksy norsy ni hilly pilly fication and means the action or habit of estimating something as worthless. There are longer medical words but medicine is almost a different language in itself. And of course there is 'supercalifragilisticexpialidocious', from the brilliant Mary Poppins.

Methionylthreonylthreonylglutaminylarginyl...isoleucine