Ferré
Il est ferré sur la géographie = He is well up in geography.
Fête
*Ce n’est pas tous les jours fête = Christmas comes but once a year.
Faire fête à quelqu’un = To welcome some one heartily.
Je me fais une fête de passer huit jours à la campagne = I look forward with pleasure to the idea of spending a week in the country.
Feu
Il n’a ni feu ni lieu = He has neither house nor home.
L’ennemi mit le pays à feu et à sang = The enemy put the country to fire and sword.
Je n’y ai vu que du feu = It was impossible for me to find out how the thing was done (as it was done so quickly); It was done so quickly (or, cleverly) that I could not make head or tail of it.