Definition of "widening"

Turning and turning in the widening gyre / The falcon cannot hear the falconer; […]

1920, William Butler Yeats, The Second Coming

She looked up sleepily and asked me what it was, and with the very words I thought she drew in her breath with a widening of the nostrils and seemed to come suddenly and fully alive.

1887, Robert Louis Stevenson, The Merry Men, Olalla

Near the site of the old Kennet Bridge signalbox, a down goods loop has been provided and this necessitated the widening of an embankment and the slewing of the up and down relief lines.

1962 October, “Talking of Trains: New signalbox at Twyford”, in Modern Railways, page 227