To me Tenuto is at the other end of the length spectrum from Staccato in all its forms. The dash over notes is used to signify that you make the extra effort to lengthen but shape and join the sounds musically without accents. Often seen under ties over repeated notes (eg Bach slow movements ) or broken slurs that group and articulate and phrase sounds more evenly without accents. You will also see dots-over-tenuto and just dots over notes used under ties and broken slurs as degrees of separation, and terms like Sostenuto and Portato. Interpreting the signs and words within each new context is a test of your musicianship and experience. Sometimes you need to bring out notes in an important slurred passage by separating the notes with Tenuto IME.
"Ordinary" bow-per-note sounds are spread somewhere in the middle of the length spectrum with perhaps more energy at the start and more release at the end in order to articulate clearly and separate them (as in in the orchestra). On-the -string bowing (no lifting off note ends, but using degrees of release) can produce clear musical sounds of any length, degree of loudness and degree of accent however Tenuto is asking for special attention and musicianship IMO.