yayo.

Unknown origin, perhaps from whimsical slang by youth. A prevailing theory, given the term's ultimate origin in Aragon and Catalan-speaking territories, is derivation from Catalan iaio (“grandpa”). It seems the first form generated was *jaja (“grandma”), from which the masculine form was derived. This would come from Catalan avia (“grandmother”) (from Latin avia), and from juvenile palatalization would generate something like *ai̯a. The common phenomenon of syllabic repetition in children's language (cf. papa, baba, etc.) would then cause the form iaia above, which would then be spread into Spanish and masculinized. Otherwise, perhaps masculinized from Greek γιαγιά (giagiá, “grandmother”).