Panini was an ancient Sanskrit grammarian born in Shalatura, modern Lahur of North-West Frontier province of Pakistan. The place is situated at a distance of four miles from Ohind near Attock on the right bank of Indus River in the ancient Kamboja|Kambojan/Gandhara|Gandharan territory. Panini is believed to have flourished in 5th century BCE, (but estimates range from the 7th to the 3rd centuries) and is famous for formulating the 3,959 sutras or rules of Sanskrit morphology (linguistics)|morphology known as the A??adhyayi. In his sutras IV.1.168-177, Panini references the Kamboja among other Kshatriya janapadas and notes it as one of the fifteen prominent Kshatriya monarchy|monarchies of the times.
Sutra IV.1.168 (janapada.shabdat.kshatriyad a�) is important. Grammer|Grammatically, it teaches that the affix a� (or �yan, i� etc) comes after a word which is both the name of a country and a Kshatriya tribe settled therein.
Here the identity of janapada and the powerful Kshatriya clans settled there is repeated. The ruling Kshatriyas inhabiting these janapadas were, as we are informed by Katyayana (2nd c BC), governed by two-fold constitutions; some were monarchies (Ekarjat) and others were republics (Sanghas).
(ii) Panchaala = name of Panchaala Kshatriya clan. Kamboja = name of Kamboja Kshatriya clan.
The above nomenclature holds good for all the Kshatriya tribes so named by Panini in sutras (4.1.168 through 4.1.177) including the Kamboja.
(iii) Panchaala + a� => Paanchaala = descendants of Panchaala Kshatriya clan.
(iv) Panchaala + a� => Paanchaala = the ruler of Panchaala Kshatriya tribe.
Thus, by adding appropriate affix (a�, �yan, i� etc) with the janapada word, the derivative to denote the descendants of Kshariyas as well as their Kshatriya rulers can be obtained for various janapadas named by Panini (4.1.168 through 4.1.177) except the Kamboja.
For Kamboja (and only the Kamboja) Panini recommends Luk (elimination) of an affix with janapada of Kamboja (sutra 4.1.175: Kambojal. Luk) which importantly informs us of an EXCEPTION for KAMBOJA, such that the Kshatriya word Kamboja does not need any affix (a�, �yan, i� etc) to be added to it to obtain a derivative to denote the descendants of Kamboja Kshatriyas as well as the Kshatryia ruler of Kambojas.
This means that the word KAMBOJA itself denotes not only (i) the Kamboja country/janapada and (ii) the Kamboja Kshatriya tribe, but, unlike other Kshatriya janapadas, it also denotes (iii) the descendants of Kamboja Kshatriyas and (iv) the Kshatriya ruler/king of the Kamboja janapada.
References: (Ancient Kamboja, People and the Country, p 29-31, Dr J. L. Kamboj; cf : Carmichael Lectures, 1918, pp 6-7, Dr D. R. Bhandarkar; Some Kshatriya Tribes of ancient India, p 234, Dr B. C. Law; Panini Kaleen Bharat (Hindi), 1955, p 61; India as Known to Panini, p 427, Dr V. S. Aggarwal; cf: Early East Iran and Atharvaveda, Persica, 1980, ffn 47, Dr Michael Witzel).
The Kambojas were a well known Republicanism|republican people since Epic Age. Mahabharata refers to several Ganah (or Republics) of the Kambojas (MBH 7/91/39). Kautiliya’s Arthashastra (11/1/4) and Ashoka's Edict No. XIII also attest that the Kambojas followed republican constitution. Panini's sutras (IV.1.168-175), though tend to convey that the Kamboja of Panini was a Kshatriya monarchy, but the special rule and the exceptional form of derivative Panini gives to denote the ruler of the Kambojas implies that the king of Kamboja was probably a titular head (king consul), probably a war leader only (Dr K. P. Jayswal, Dr J. L. Kamboj).
References: (Carmichael Lectures, p 6-7, Dr D. R. Bhandarkar; Kshatriya Tribes of ancient India, p 234, Dr B. C. Law; Ancient Kamboja, People and the Country, p 30, Dr J. L. Kamboj) .
Kamboja + a� => Kaamboja where Kaamboja denotes the ancestral homeland of the Kambojas.
The above referred to derivative names for animal/plant/mineral etc, native to or imported from Kamboja, are in accordance with the principles of Linguistics which teaches that a special product imported from a certain country or else native to a certain place gets named after that country/place.
But in spite of Panini's above rules for correct usage of Sanskrit, both Kamboja as well as Kaamboja have yet been used indiscriminately without any change in meaning. We rather see Kaamboja being mostly used in the texts like Ramayana, Mahabharata and all post-Panini|Paninian Sanskrit literature in the same sense as Kamboja.
Sanskrit: Kamboja-mundah Yavana-mundah i.e shaved headed Kambojas, shaved headed Yavanas.