| Subject | English | Icelandic |
| math. | Bock's three component model | þrjú Bock's hluti líkansins |
| math. | cubic designs with three associate classes | rúmmetra hönnun með þremur félagi bekkjum |
| comp., MS | three-dimensional | þrívítt (Of, pertaining to, or being an object or image having or appearing to have all three spatial dimensions (length, width, and depth)) |
| math. | three-dimensional lattice | tridimensional grindarbyggingu |
| bot. | three-flowered rush | blómsef (Juncus triglumis L.) |
| bot. | three-leaved rush | móasef (Juncus trifidus L.) |
| math. | three-point assay | þrjá punkta prófi |
| math. | three-series theorem | þriggja röð setningin |
| math. | three-stage least squares | þriggja þrepa kosti ferninga |
| comp., MS | three-way matching policy | þríhliða jöfnunarregla (A matching policy that requires one or more vendor invoice prices to match with one or more purchase order prices and that requires one or more vendor invoice quantities to match with one or more product receipt quantities) |