SAUNDARANANDA 1.22: Becoming Gautama (Nominally)

teShaaM munir upaadhyaayo
gautamaH kapilo 'bhavat
guru-gotraad ataH kautsaas
te bhavanti sma gautamaaH

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1.22
The sage Kapila Gautama

Became their preceptor;

And so from the guru's surname

Those Kautsas became Gautamas --

COMMENT:
This explains how the Buddha's royal ancestors, whose original surname was Kautsa, came to be called Gautama: the tradition is that they took the surname from Kapila Gautama, the champion of asceticism in whose forest ashram they went to live.

We primarily desire to know how Shakyamuni became Shakyamuni, how Siddhartha became Siddhartha -- how Gautama Buddha became Gautama Buddha in the true sense.

To satisfy this desire, Ashvaghosha provides us in Canto 3 with his own description of how Gautama became Gautama. And Cantos 12 through 16 are Gautama's own description of the means-whereby a Gautama becomes a Gautama.

Before examining Gautama's becoming Gautama in real terms, however, Ashvaghosha, leaving no stone unturned, is presenting here in nominal terms a history of how the Gautamas became the Gautamas.

EH Johnston:
The seer, Kapila Gautama, became their preceptor ; hence, following their guru's gotra, they were turned from Kautsas into Gautamas ;

Linda Covill:
The sage Kapila Gautama became their guru, and because of their guru's clan, they who had been Kautsas became Gautamas,

VOCABULARY:
teShaam (gen. pl.): of them
muniH (nom. sg.): m. sage
upaadhyaayaH (nom. sg.): m. a teacher , preceptor (who subsists by teaching a part of the veda or vedaaNgas , grammar &c ; he is distinguished from the aacaarya)

gautamaH (nom. sg. m.): Gautama
kapilaH (nom. sg. m.): Kapila
abhavat (3rd pers. sg. imperfect bhuu): he became

guru-gotraad (abl.): from the guru's family name
guru: m. any venerable or respectable person; m. a spiritual parent or preceptor
gotra: n. " family enclosed by the hurdle " , family , race , lineage , kin; family name ; name (in general)
ataH: ind. hence
kautsaaH (nom. pl.): Kautsas
kautsa: mfn. relating to kutsa
kutsa: m. N. of a RShi (called aarjuneya , author of several hymns of the RV. ; when attacked by the demon shuShNa , indra defended him and killed the demon ; but in other hymns, kutsa is represented as persecuted by indra) ; N. of a descendant of aNgiras (author of hymns of the RV) ;
lightning , thunderbolt ; pl. the descendants or the family of kutsa

te (nom. pl.): they
bhavanti (3rd pers. pl. bhuu): they became
sma: ind. a particle perhaps originally equivalent to " ever " , " always "
and later to " indeed " , " certainly " , " verily " , " surely " (it is often used pleonastically)
gautamaaH (nom. pl.): Gautamas