THERMIONIC Meaning of THERMIONIC in English thermionic BrE AmE ˌθɜːm i ˈɒn ɪk ◂ AmE \ ˌθɝːm i ˈɑːn ɪk ◂▷ thermionic|s s▶ ˌ thermi ˌ onic ˈ valve BrE AmE Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012