fa ‧ mil ‧ i ‧ ar ‧ ly /fəˈmɪliəli $ -liərli/ BrE AmE adverb
[ Word Family: noun : ↑ familiarity ≠ ↑ unfamiliarity , ↑ family , ↑ familiarization ; adjective : ↑ familiar ≠ ↑ unfamiliar , ↑ familial ; verb : ↑ familiarize ; adverb : ↑ familiarly ]
in an informal or friendly way:
Charles, familiarly known as Charlie