French word fermer comes from Proto-Indo-European *dʰerw-, and later Latin firmus (Faithful, steadfast, true. Stable, strong, firm.)
*dʰerw- (Proto-Indo-European)
*dʰer-mo-s (Proto-Indo-European)
firmus (Latin)
Faithful, steadfast, true. Stable, strong, firm.
firmo (Latin)
I make firm, strengthen, harden, fortify.
fermer (French)
To close. To shut.