Definition of "grinningly"

Squeaker's dog sniffed and barked joyfully around them till his licking efforts to bottom a salmon tin sent him careering in a muzzled frenzy, that caused the younger woman's thick lips to part grinningly till he came too close.

1902, Barbara Baynton, edited by Sally Krimmer and Alan Lawson, Bush Studies (Portable Australian Authors: Barbara Baynton), St Lucia: University of Queensland Press, published 1980, page 21

It’s very funny — Bob is played by Bill Murray at his most unhinged, the psychiatrist by Richard Dreyfuss at his most grinningly uptight — but it’s a little creepy too.

2009 July 19, Terrence Rafferty, “On the Screen, the Shrink Has Shrunk”, in New York Times‎