mainly, mostly, chiefly
C'était principalement des femmes.
They were mainly women.
C'est principalement là-dessus que vous devez concentrer votre attention.
That is primarily what you should focus your attention on.
Son succès a été principalement dû à la bonne fortune.
His success was mainly due to good fortune.
La force de Cao réside principalement dans son infanterie.
Cao's strength lies primarily in his infantry.
— Les 3 Royaumes (2008)
Mostly about me.
L'objectif est d'éloigner le faible et, principalement, le corrompu.
The objective is to keep the weak, and primarily the corrupt, at a distance.
— Troupe d'Élite (2007)