Why not the base, both "base" and "common" are antonyms or noble :^)
No, it needs glide-reflection symmetry on one axis like the waveform you get by low-passing a square-wave: _ ____ R __ __ | | | ---/\/\/---+------ .' \ .' |____| |__ | / `.__/ ===== C |----t----| | --+-- ///// RC < t
In the frequency domian saying inversion is the same as 180deg phase shift is completely accurate, in the time domain it sometimes works..
Still ambiguous.