[pe-troh-jen-uh-sis] /ˌpɛ troʊˈdʒɛn ə sɪs/ noun 1. the branch of petrology dealing with the origin and formation of rocks. 2. the origin and formation of rocks. petrogenesis (pět’rō-jěn’ĭ-sĭs) The branch of petrology that deals with the origin and formation of rocks, especially igneous rocks.
[pe-truh-glif] /ˈpɛ trəˌglɪf/ noun 1. a drawing or carving on rock, made by a member of a prehistoric people. /ˈpɛtrəˌɡlɪf/ noun 1. a drawing or carving on rock, esp a prehistoric one n. 1870, from French pétroglyphe, from Greek petra “rock” (see petrous) + glyphe “carving” (see glyph).
[pe-truh-grad; Russian pyi-truh-graht] /ˈpɛ trəˌgræd; Russian pyɪ trʌˈgrɑt/ noun 1. former name (1914–24) of (def 2). /ˈpɛtrəʊˌɡræd; Russian pɪtraˈɡrat/ noun 1. a former name (1914–24) of Saint Petersburg