From Longman Dictionary of Contemporary Englishsidelongside‧long /ˈsaɪdlɒŋ $ -lɒːŋ/ adjective → sidelong look/glance —sidelong adverb ‘You looked very well this morning, ’ she added, glancing sidelong at him.
Examples from the Corpus
sidelong• He looked sidelong at her with a quick smile, and she frowned and nodded his attention quickly towards the stranger.• She cast a sidelong glance at Fen.• I cast a sidelong glance, to see if she's noticed.• Jean-Claude's sidelong half-smile had felt congratulatory.• He kept watching her with a delighted, sidelong smile as if she constantly astonished him.• Cynan flew to pin the struggling legs, and Meurig slid sidelong through the trees to help him. 