Home › Words › U › underjoinunderjoinunderjoin means to join, add, or append (something) to the end of something else.Among words judged in Lexicurio's Arena, underjoin ranks #11,704 of 42,762 for Qualifying.EtymologyFrom Middle English underjoinen, equivalent to under- + join.verbTo join, add, or append (something) to the end of something else.e.g.“Near-synonym: annex”Definitions & examples from Wiktionary (CC BY-SA 3.0).