Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Pan- \Pan-\, Panta- \Pan"ta-\, Panto- \Pan"to-\ [Gr. ?, m., ?, neut., gen. ?, all.] Combining forms signifying all, every; as, panorama, pantheism, pantagraph, pantograph. Pan- becomes pam- before b or p, as pamprodactylous.
Douglas Harper's Etymology Dictionary
word-forming element meaning "all, every, whole, all-inclusive," from Greek pan-, combining form of pas (neuter pan, masculine and neuter genitive pantos) "all," from PIE *pant- "all" (with derivatives found only in Greek and Tocharian).\n
\nCommonly used as a prefix in Greek, in modern times often with nationality names, the first example of which seems to have been Panslavism (1846). Also panislamic (1881), pan-American (1889), pan-German (1892), pan-African (1900), pan-European (1901), pan-Arabism (1930).
pre. A combining form meaning "all", used in the formation of compound words.