I did some research a few years back on Brahmā Sahampati, and concluded that the name 'Sahampati' did not directly mean anything. Only in the Pali tradition does this particular Brahmā ask the Buddha to teach. But the name does seem to include elements from brahmanical (pre-Hindu) mythology. Here is an extract from my article on the topic:
"In the Dharmaguptaka and Mahīśāsaka Vinayas, as well as in the Mahāvastu (Mvu III 317) and the Lalitavistara, in passages very similar to the episode in the Pāli canon, the Brahmā who requests the Buddha to teach is simply called Brahmā or Mahā-Brahmā, and is not specifically named. In the Pāli tradition, however, this Brahmā is given the name Sahampati. In a short discourse in the Saṃyutta Nikāya, we discover that Brahmā Sahampati was a bhikkhu named Sahaka under the previous Buddha Kassapa, reborn in this kalpa according to his merit (SN V 233). This leads the commentary (p.11) on the Buddhavaṃsa to say that his name should be Sahakapati (Haldar 1977: 97). This, however, would appear to be an over-literal reading by the commentator; it seems more likely that the name Sahaka is derived from the name Sahampati. The name Sahampati itself is mysterious, which is perhaps why the commentator offered his derivation.
"Rhys Davids and Oldenberg suggested that ‘Sahampati’ could be understood as equivalent to the Sanskrit ‘Svayampati’ (Rhys Davids 1881: 86). This name does not appear to be found in the epics and Purāṇas, but it combines two names commonly used in them for Brahmā. ‘Svayambhū’, meaning ‘Self-existent’, is an epithet for a deity believed to be eternal and supreme; ‘Svayambhuva Manu’ was born of Brahmā and Sarasvatī and represents the Vedas (Khan 1981: 30, 38). ‘Pati’ means ‘Lord’; ‘Prajāpati’, ‘Lord of Creation’ is another epithet for Brahmā, and becomes a name for sons of Brahmā (Khan 1981: 39). ‘Sahampati’, understood as the Pāli version of ‘Svayampati’, thus combines recognisable elements from well-known epithets for the Brahmā of Indian mythology. The early Buddhist story-tellers clearly wished the Sahampati who requested the Buddha to teach to be regarded as the same Brahmā worshipped by their non-Buddhist religious contemporaries."
(From Dhivan Thomas Jones, 'Why Did Brahmā Ask the Buddha to Teach?', in Buddhist Studies Review 26:1 (2009)).
All the best with your research.
Dhivan
www.dhivan.net
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