Pallavi literally means 'sprout', a vegetation image associated in Indian symbol systems with rasa (sap, juice flavour, essential inspiring vitality) and it carries a sense of a beginning. It suggests the idea of a seed and a shoot, or a bud, the beginning of efflorescence and the stem resource for an expansion. Until Subbarama Dikshitar's time (he published Sangita Sampradaya Pradarshini in 1904), it was usually called pallava. One traditional etymology breaks the word into three syllables and derives each from a component of a song: padam (‘word’), layam (‘rhythm’), vinyasam (‘display’). T S Parthasarathy has called this a mere ‘guess’, but perhaps this playful derivation could be understood more as a helpful invention, a mnemonic or pedagogical device, rather than literal linguistic etymology or erroneous speculation. It sums up the parts of the nucleus in a nutshell. From the pallavi, the embryonic original impulse, and so the essential spirit of the work, the whole of the kriti develops.
Before the term pallavi came to be associated with the initial line of Tyagaraja’s kritis it was the term for the dominant form of Karnataka musical court performances in pre-Tyagaraja times. Designated more fully as ragam–tanam–pallavi, or simply called pallavi, it was one expression of manodharma (the duty of the mind’, exercise of the imagination) sangita, the improvisational art music of the times. The reason why this form, which often extended for many hours, was called pallavi, probably had to do with the single line of text around which it was musically elaborated. This form was used in lengthy competitive exhibitions of musical technique, including displays of rhythmic and melodic virtuosity and improvisation on the theme.
Jackson, William (1991), Tyagaraja: Life and Lyrics, Oxford University Press, London, 473-474.