Fil vs. tranchant
The French language has many terms that articulate nuances, especially in the context of descriptions. 'Fil' and 'tranchant' are such terms with specific uses when referring to edges or cutting elements, particularly of blades.
Fil
'Fil' primarily refers to the very edge or sharp part of a blade that is intended for cutting. It is not just limited to the concept of an edge but emphasizes the sharpness and the cut it is designed to make.
Le couteau a perdu son fil après une utilisation intensive.
(The knife has lost its sharpness after intensive use.)
Affûte bien le fil de ta lame avant de commencer à couper.
(Sharpen the edge of your blade well before starting to cut.)
Je me suis coupé avec le fil de la feuille.
(I cut myself on the paper's edge.)
Tranchant
'Tranchant' is used to describe the cutting edge of a blade more broadly. It emphasizes the capability of the edge to cut, rather than just its sharp aspect. 'Tranchant' can be used metaphorically as well, implying something or someone is incisively effective or keen.
L'épée avait un tranchant imparable qui pouvait fendre une armure en deux.
(The sword had an unstoppable cutting edge that could split armor in two.)
Son esprit tranchant lui permet de résoudre les problèmes rapidement.
(His sharp mind allows him to solve problems quickly.)
Ce couteau a un bon tranchant; il coupe les tomates sans effort.
(This knife has a good cutting edge; it slices tomatoes effortlessly.)
Summary
'Fil' and 'tranchant' both refer to edges, especially on blades, but with slight nuances. 'Fil' emphasizes sharpness and cutting potential, often referring to precision tools or fine edges. 'Tranchant', on the other hand, denotes the broad ability of an edge to cut through materials and can be used metaphorically for effectiveness beyond physical edges.