expatiate
Concise Oxford English Dictionary © 2008 Oxford University Press:
expatiate /ɪkˈspeɪʃɪeɪt, ɛk-/
▶verb (expatiate on) speak or write in detail about.
– derivatives
expatiation noun.
expatiation noun.
– origin C16: from L. exspatiari ‘move beyond one's usual bounds’ (based on spatium ‘space’).
'expatiate' also found in these Oxford entries:

