comenzar, empezar, principiar
It seems comenzar & empezar are interchangeable, how is principiar different'
"Empezar" and "comenzar" are pretty close in their meaning, although "comenzar" is preferred in more formal speech, and "empezar" can also be used to for "start to eat something". "Principiar" is extremely rare in Spain except in literature, so you could use it there if you wanted to shock people with an unusual word. You also have "iniciar", which is similar, but it is not as flexible as "empezar" and "comenzar", e.g. you can't say "El partido ha iniciado".