From Ondrej Sefcik (6.06):

The surname 'Masaryk' is not in fact of Czech origin, but Slovak
one, but it is very similar to common Czech surname Masaøík. Both
surnames are derived from Slovak masar and Czech dialectal (Moravian and
Silesian) masaø "butcher" (derived from maso "meat"). Derivative suffix
-yk or -ík has deminutive meaning, so Masaryk means in Slovak (but is
sounds so in Czech ears) "little butcher".

PS: There is a Czech word masaøka, Slovak masarka, which means "Blowfly
with iridescent blue body; makes a loud buzzing noise in flight"