Meaning

adjective (used especially of glances) directed to one side with or as if with doubt or suspicion or envy; - Elizabeth Bowen

adjective situated at or extending to the side; ; - Tennyson

adjective inclining or directed to one side; - Bram Stoker

origin1520s, from Middle English sidlyng (early 14th century), from side + -lyng (“(frequentative)”) (modern English -le (“(frequentative)”)). Reanalyzed as side + long.

Etymology from Wiktionary, CC BY-SA 3.0