tierce
n.
5ME terce < OFr < L tertia, fem. of tertius, (a) third < base of tres, THREE6
1 orig., a third
2 [often T3] TERCE
3 an old unit of liquid measure, equal to R pipe (42 gallons)
4 a cask of this capacity, between a barrel and a hogshead in size
5 Fencing the third defensive position, from which a lunge or parry can be made

The only way I remember seeing this word is the fencing term.