| ISOTOPE | Each of two or more forms of the same element |
| ALLOTROPY | The existence in the same state of more than one form of the same element with different properties |
| ISOTOPIC | Like different forms of the same element |
| PRONG | One of the tines of a fork; or, by extension, each of two or three parts of an attack or operation (5) |
| ISOTOPES | Varieties of the same element with different numbers of neutrons (8) |
| ISOMER | Each of two or more compounds with the same formula but different arrangements of atoms (6) |
| ALLOTROPE | Each of two or more different forms in which an element can exist (9) |
| TRIGON | Old word for a three-sided polygon, such as an isosceles example; an ancient Greek or Roman lyre or harp; or, a group of three astrological signs belonging to the same element (6) |
| LOBE | A roundish, flattish projection or pendulous part often each of two or more such parts divided by a fissure |
| MUTUAL | Concerning each of two or more people (6) |
| CORRELATE | Each of two or more connected things (9) |
| VARIANT | A form of something that differs in some respect from other forms of the same thing (7) |
| NYNORSK | What is one of the two official forms of the Norwegian language that is based on the dialects of wes |
| EITHER | Each of two, or one in three bananas |
| PHASE | Any of the cyclically recurring forms of the moon or a planet, resulting from surface illumination by the Sun (5) |
| BOKMAL | One of the two main forms of the Norwegian language, alongside Nynorsk (6) |
| REBEC | One of the earliest forms of the violin |
| HOMONYM | Each of two words spelled or said the same but with different meanings |
| SPANISH | Language in which the first words to answers of asterisked clues are forms of the verb "to be" (7) |
| COMMERCE | The activity embracing all forms of the purchase and sale of goods and services (8) |
