Datta, Dayadvam, Damyata and are Sanskrit terms. In his notes on The Wasteland, Eliot identifies the phrases as coming from the Brihidaranyaka Upanishad. (The Upanishads are are set of holy books written in the Hindu tradition.)
Eliot translates these terms in his notes as follows:
- Datta: Give
- Dayadvam: Sympathize
- Damyata: Control
Control here commonly is understood to refer to self-restraint.
These terms are explored in the text with each phrase appearing at the head of its own stanza. In each stanza the idea behind the term is briefly, if obscurely, elucidated.
The terms come from a story from the above mentioned Upanishad wherein men, gods and demons approach Brahman (in the form of thunder here) and ask for guidance.
According to the Indian legend, men, gods, and devils ask the thunder the same question, and each is given a different answer—give, sympathize, and control, respectively.
The guidance each receives is exactly the same, "Da", but later is interpreted differently according to the needs and nature of each group.