At first sight

the power or faculty of seeing; perception of objects by use of the eyes; vision.
an act, fact, or instance of seeing.
one’s range of vision on some specific occasion:
Land is in sight.
a view; glimpse.
mental perception or regard; judgment.
something seen or worth seeing; spectacle:
the sights of London.
Informal. something unusual, surprising, shocking, or distressing:
They were a sight after the fight.
Commerce.

presentation of a bill of exchange:
a draft payable at two months after sight.
a showing of goods, especially gems, held periodically for wholesalers.

Older Use. a multitude; great deal:
It’s a sight better to work than to starve.
an observation taken with a surveying, navigating, or other instrument to ascertain an exact position or direction.
any of various mechanical or optical viewing devices, as on a firearm or surveying instrument, for aiding the eye in aiming.
Obsolete. skill; insight.
to see, glimpse, notice, or observe:
to sight a ship to the north.
to take a sight or observation of (a stake, coastline, etc.), especially with surveying or navigating instruments.
to direct or aim by a sight or sights, as a firearm.
to provide with sights or adjust the sights of, as a gun.
to aim or observe through a sight.
to look carefully in a certain direction.
at first sight, at the first glimpse; at once:
It was love at first sight.
at sight,

immediately upon seeing, especially without referring elsewhere for assurance, further information, etc.:
to translate something at sight.
Commerce. on presentation:
a draft payable at sight.

catch sight of, to get a glimpse of; espy:
We caught sight of the lake below.
know by sight, to recognize (a person or thing) seen previously:
I know him by sight, but I know nothing about him.
not by a long sight, Informal. definitely not:
Is that all? Not by a long sight.
on / upon sight, immediately upon seeing:
to shoot him on sight; to recognize someone on sight.
out of sight,

beyond one’s range of vision.
Informal. beyond reason; exceedingly high:
The price is out of sight.
Slang. (often used as an interjection) fantastic; marvelous: a ceremony so glamorous it was out of sight.
Oh wow! Out of sight!

sight for sore eyes, someone or something whose appearance on the scene is cause for relief or gladness.
sight unseen, without previous examination:
to buy something sight unseen.
noun
the power or faculty of seeing; perception by the eyes; vision related adjectives optical visual
the act or an instance of seeing
the range of vision: within sight of land
range of mental vision; point of view; judgment: in his sight she could do nothing wrong
a glimpse or view (esp in the phrases catch sight of, lose sight of)
anything that is seen
(often pl) anything worth seeing; spectacle: the sights of London
(informal) anything unpleasant or undesirable to see: his room was a sight!
any of various devices or instruments used to assist the eye in making alignments or directional observations, esp such a device used in aiming a gun
an observation or alignment made with such a device
an opportunity for observation
(obsolete) insight or skill
(informal) a sight, a great deal: she’s a sight too good for him
a sight for sore eyes, a person or thing that one is pleased or relieved to see
at sight, on sight

as soon as seen
on presentation: a bill payable at sight

know by sight, to be familiar with the appearance of without having personal acquaintance: I know Mr Brown by sight but we have never spoken
(informal) not by a long sight, on no account; not at all
out of sight

(slang) not visible
extreme or very unusual
(as interj.): that’s marvellous!

set one’s sights on, to have (a specified goal) in mind; aim for
sight unseen, without having seen the object at issue: to buy a car sight unseen
verb
(transitive) to see, view, or glimpse
(transitive)

to furnish with a sight or sights
to adjust the sight of

to aim (a firearm) using the sight
n.

Old English sihð, gesiht, gesihð “thing seen; faculty of sight; aspect; vision; apparition,” from Proto-Germanic *sekh(w)- (cf. Danish sigte, Swedish sigt, Middle Dutch sicht, Dutch zicht, Old High German siht, German Sicht, Gesicht), stem that also yielded Old English seon (see see (v.)), with noun suffix -th (2), later -t.

Verily, truth is sight. Therefore if two people should come disputing, saying, ‘I have seen,’ ‘I have heard,’ we should trust the one who says ‘I have seen.’ [Brhadaranyaka Upanishad 5.14.4]

Meaning “perception or apprehension by means of the eyes” is from early 13c. Meaning “device on a firearm to assist in aiming” is from 1580s. A “show” of something, hence, colloquially, “a great many; a lot” (late 14c.). Sight for sore eyes “welcome visitor” is attested from 1738; sight unseen “without previous inspection” is from 1892. Sight gag first attested 1944. Middle English had sighty (late 14c.) “visible, conspicuous; bright, shining; attractive, handsome;” c.1400 as “keen-sighted;” mid-15c. as “discerning” (cf. German sichtig “visible”).

v.

1550s, “look at, view, inspect,” from sight (n.). From c.1600 as “get sight of,” 1842 as “take aim along the sight of a firearm.” Related: Sighted; sighting.

sight (sīt)
n.

The ability to see.

Field of vision.

sight for sore eyes, a
sight unseen

also see:

at first blush (sight)
at sight
can’t stand the sight of
catch sight of
heave into sight
in sight
know by sight
lose sight of
love at first sight
lower one’s sights
on sight
out of sight
raise one’s sights
second sight
see the sights
set one’s sights on
twenty-twenty hindsight