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Concise Oxford English Dictionary
squint
■ verb
look at someone or something with partly closed eyes. ▶partly close (one’s eyes).
have a squint affecting one eye.
■ noun
a permanent deviation in the direction of the gaze of one eye.
informal a quick or casual look.
an oblique opening through a wall in a church permitting a view of the altar.
■ adjective chiefly Scottish not straight or level.

squinter noun
squinty adjective

C16: shortening of asquint.
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Concise Oxford Thesaurus
squint
▶ verb
the sun made them squint: SCREW UP ONE’S EYES, narrow one’s eyes, peer, blink.
he has squinted from birth: BE CROSS-EYED, have a squint, suffer from strabismus; Scottish be skelly; Brit. informal be boss-eyed.
▶ noun
(informal) we must have another squint at his record card: LOOK, glance, peep, peek, glimpse; view, examination, study, inspection, scan, sight; informal eyeful, dekko, butcher’s, gander, look-see, once-over, shufti.
does he have a squint?: CROSS-EYES, strabismus; Brit. informal boss-eye.
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Merriam-Webster Collegiate® Dictionary
1squint
Pronunciation: ‘skwint
Function: adjective
Etymology: Middle English asquint
Date: 1579

1 of an eye : looking or tending to look obliquely or askance (as with envy or disdain)
2 of the eyes : not having the visual axes parallel : CROSSED
2squint
Function: intransitive verb
Date: 1599

1 a : to have an indirect bearing, reference, or aim b : to deviate from a true line
2 a : to look in a squint-eyed manner b : to be cross-eyed c : to look or peer with eyes partly closed
transitive verb : to cause (an eye) to squint
–squint·er noun
–squint·ing·ly \’skwin-tiŋ-lē\ adverb
3squint
Function: noun
Date: circa 1652

1 : STRABISMUS
2 : an instance of squinting
3 : HAGIOSCOPE
–squinty \’skwin-tē\ adjective
stra·bis·mus
Pronunciation: strə-‘biz-məs
Function: noun
Etymology: New Latin, from Greek strabismos condition of squinting, from strabizein to squint, from strabos squint-eyed; akin to Greek strephein to twist
Date: circa 1684

: inability of one eye to attain binocular vision with the other because of imbalance of the muscles of the eyeball ― called also squint ― compare CROSS-EYE
–stra·bis·mic \-mik\ adjective