1570s, from side (n.) + way (n.), with adverbial genitive. To look sideways "cast scornful glances" is recorded from 1844.
turned sideways to show the profile
a picture lit sideways
leaning sideways
the car slipped sideways into the ditch
side-swipe
side-table
sidetrack
sidewalk
side-way
sideways
sidewinder
Sidhe
siding
sidle
Sidon
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