A helpful picture for fillet is one long narrow strip, much thinner than whatever lies on either side of it. Tie that strip round a head and it holds the hair. Lay it between two bands on a column and it becomes the quiet plain line between them. Press it into the corner where a wall meets a floor and it seals the joint. Lift it off the bones of a fish and it is the piece you cook. Every use of the word is somebody pointing at a long thin strip and naming it.
From Latin fīlum, 'thread', through Old French filet, a little thread or narrow band. The thread is still visible in every modern use.
來自拉丁文 fīlum（線），經古法文 filet（小小的線、細帶）進入英文。那條「線」的畫面，在今天每一個用法裡都還看得見。
Wiktionary etymology_text supplied in this packet (kaikki:3f6f69a190036ae4:719010196)
Three branches
細細的一條（帶子、線腳、填縫）
最貼著核心畫面的一支：東西本身就是那條細長的帶子。
noun · C2
A thin narrow strip or band of material, used in building, woodworking and design: for example a plain strip of wood or plaster running between two wider decorated parts, or a line of sealant laid along the inside corner where a wall meets a floor.
細條、細帶（建築、木工、裝飾用語）
肉上的那一條
把刀沿著骨頭滑過去，掀下來的也是一長條——只是這次那條東西是肉。
noun · B2
A piece of meat or fish with the bones taken out, usually cut long and flat so that it can be cooked and eaten in one piece. In British use it also names a tender cut of beef from below the lower back, the one Americans call tenderloin.
去骨的魚排、肉排；（英式）里肌、腓力
角落裡的那一條弧
一條材料填進內角，把尖角補成圓的——仍然是「一條」，只是這次它躲在兩個面相交的地方。
noun · C2
In engineering and technical drawing, a small rounded shape added where two surfaces meet at an inside corner, so that the corner is smooth and curved instead of sharp.
圓角（工程、製圖用語）
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
filletnoun/ˈfɪl.ɪt/
archaicA headband; a ribbon or other band used to tie the hair up, or keep a headdress in place, or for decoration.
A thin strip of any material, in various technical uses.
businessconstructionmanufacturingA heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet.
CADcomputingdraftingA rounded relief or cut at an edge, especially an inside edge, added for a finished appearance and to break sharp edges.
A strip or compact piece of meat or fish from which any bones and skin and feathers have been removed.
A premium cut of meat, especially beef, taken from below the lower back of the animal, considered to be lean and tender; also called tenderloin.
architectureA thin featureless moulding/molding used as separation between broader decorative mouldings.
architectureThe space between two flutings in a shaft.
governmentheraldryhobbiesAn ordinary equal in breadth to one quarter of the chief, to the lowest portion of which it corresponds in position.
The thread of a screw.
A colored or gilded border.
The raised moulding around the muzzle of a gun.
artsbusinesscarpentryAny scantling smaller than a batten.
anatomymedicinesciencesA fascia; a band of fibres; applied especially to certain bands of white matter in the brain.
The loins of a horse, beginning at the place where the hinder part of the saddle rests.
filletverb/ˈfɪl.ɪt/
To slice, bone or make into fillets.
To apply, create, or specify a rounded or filled corner to.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。