To the thread of the water; to the central line, or middle of the stream. Usque ad filum agues, as far as the thread of the stream. Bract, fol. 2086; 235a. A phrase of frequent occurrence in modern law; of which ad medium filum aguw (g. v.) is another form. AD FXLUM Vta:. To the middle of the way; to the central line of the road. Parker v. Inhabitants of Framingham, 8 Mete. (Mass.) 260.