The Collaborative International Dictionary of English v.0.48:
Mavournin \Ma*vour"nin\, Mavourneen \Ma*vour"neen\ (m[.a]*v[=oo]r"n[=e]n), n. [Ir. mo mhuirnin my darling; mo my + mhuirnin darling.] My darling; -- an Irish term of endearment for a girl or woman. "Erin mavournin." --Campbell. [Webster 1913 Suppl.]