1570s, "looking different ways; looking obliquely," shortened form of asquint (adv.). Meaning "looking indirectly" is from 1610s.
1590s, from squint (adj.). Related: Squinted; squinting.
"non-coincidence of the optic axes," 1650s, from squint (adj.). Meaning "sidelong glance" is from 1660s.
The children squinted so as to scare each other
The driver squinted as the sun hit his windshield