ompa.

Headword: 
ompa.
Principal English Translation: 

there (location), then (temporal); generally means farther away than "oncan" but both can mean "de allá"; at... (an indication that a big phrase or location is coming up; an expression that tells "where")

Orthographic Variants: 
onpa
IPAspelling: 
oːmpɑ
Alonso de Molina: 

ompa. alla, o de alla, alli, o de alli.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 76v. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

ŌMPA there (distal) / allá, o de allá (C) T consistently has a short vowel in the first syllable. See ŌN, -PA.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 179.

Horacio Carochi / English: 

ōmpa=there
Horacio Carochi, S.J., Grammar of the Mexican language with an explanation of its adverbs (1645), translated and edited with commentary by James Lockhart, UCLA Latin American Studies Volume 89 (Stanford: Stanford University Press, UCLA Latin American Center Publications, 2001), 508.

Andrés de Olmos: 

Nepa, ompa, nechca, nechcapa, alli, de alli, por alli, a alli, o aculla, de aculla, por aculla, a aculla.
Andrés de Olmos, Arte para aprender la lengua Mexicana, ed. Rémi Siméon, facsimile edition ed. Miguel León-Portilla (Guadalajara: Edmundo Aviña Levy, 1972), 188.

Lockhart’s Nahuatl as Written: 

particle. there (more distant than oncān). in ōmpa, where. ōn, pa. 228
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 228.

Attestations from sources in English: 

also spelled onpa
Thelma Sullivan, Documentos Tlaxcaltecas del siglo XVI en lengua náhuatl (Mexico: Universidad Nacional Autónoma de México, 1987), 30.

oc ompa = at that time, then
can also indicate where we will go looking (i.e. the future)
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.

in ompa, yn ompa = where (not as a question), there
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.

Attestations from sources in Spanish: 

çan ye ompa = del mismo lugar (Tetzcoco, 1624)
Benjamin Daniel Johnson, “Transcripción de los documentos Nahuas de Tezcoco en los Papeles de la Embajada Americana resguardados en el Archivo Histórico de la Biblioteca Nacional de Antropología e Historia de México”, en Documentos nahuas de Tezcoco, Vol. 1, ed. Javier Eduardo Ramírez López (Texcoco: Diócesis de Texcoco, 2018), 166–167.