side ‧ long /ˈsaɪdlɒŋ $ -lɒːŋ/ BrE AmE adjective
sidelong look/glance a way of looking at someone by moving your eyes to the side, especially so that it seems secret, dishonest, or disapproving:
He gave Oliver a sidelong glance.
—sidelong adverb :
‘You looked very well this morning,’ she added, glancing sidelong at him.