Everything on this post is from Chapter 6 abhidhammatthasangaha http://www.buddhanet.net/pdf_file/abhidhamma.pdf
" onclick="window.open(this.href);return false;
Some diacritics changed letters in transit.
8. Mahabhutani—lit., those that have grown great. The four great Essentials are the fundamental material elements which are inseparable. Every material substance, ranging from the minutest particle to the most massive object, consists of these four elements which possess specific characteristics.
17. Photthabba—owing to its subtlety, the element of cohesion (àpo/water) cannot be felt by the sense of touch.
Only the other three Fundamental Elements are regarded as tangible. In water, for instance, the cold felt is tejo, the softness is pañhavi, and the pressure is vàyo. One cannot touch àpo as its property is cohesion.
9. Upàdàya-rupàni—Derivative or secondary material properties dependent on the Great Essentials. Like the earth are the Essentials; the Derivatives are like trees that spring therefrom. The remaining 24 råpas are
regarded as Derivatives.
10. Patthavi-dhàtu—The pàli term dhàtu means that which bears its own characteristic marks. Element is the closest equivalent for dhàtu. Pañhavi-dhàtu, literally, means the earth-element. It is so called because like the earth it serves as a support or foundation for the other coexisting råpas. Pañhavã (Saüskrt prñhivi), also spelt pathavi, puthavi, puthuvi, puñhuvi—is derived from puth, to expand, to extend. So far, though not very satisfactory the closest equivalent for pañhavi-dhàtu is ‘the element of extension’. Without it objects cannot occupy space. Both hardness and softness are characteristics of this element.
11. âpo-dhàtu—lit., the fluid element. âpo is derived from√ ap, to arrive, or from à +√ pày, to grow, to increase. It is ‘the element of cohesion.’ According to Buddhism it is this element that makes different particles of matter cohere, and thus prevents them from being scattered about. Both fluidity and contraction are the properties of this element. It should be understood that cold is not a characteristic of this element.
12. Tejo-dhàtu—lit., the fire-element is explained as ‘the element of heat’. Tejo is derived from √ tij, to sharpen, to mature. Vivacity and maturity are due to the presence of this element. Both heat and cold are the properties of tejo. Intense tejo is heat, and mild tejo is cold. It should not be understood that cold is the characteristic of àpo and heat is that of tejo; for, in that case, both heat and cold should be found together as àpo and tejo coexist.
13. Vàyo-dhàtu—lit., ‘the air-element’, is explained as the element of motion. Vàyo is derived from √ vày, to move, to vibrate. Motion, vibration, oscillation, and pressure are caused by this element.