only, sole: the one and only of its kind, and so uniquely precious or utterly alone
TranslatabilityApproximateCertaintyStrong
This word marks something as the single one there is. From that one idea it fans out in three directions, depending on who or what is the only one:
an only child, a parent's single offspring, and therefore irreplaceable
a person left solitary, the only one present, and therefore lonely
one's own life, spoken of as the only life a person has, and therefore worth guarding above all
The thread running through all three is singleness that makes a thing precious. An only child cannot be replaced; a solitary person has no one else; the one life a person holds is the only one they will ever get.
The most famous case is the word applied to Isaac in Genesis 22, "your only son," where it carries the whole weight of what Abraham is asked to give up. That verse also shaped later Christian language: Greek translators reached for "beloved" and "one and only" (μονογενής) to render it, which is how the idea travels into the New Testament.
Nuances
1aan only child: a parent's single offspring, and so uniquely precious
TranslatabilityDirect
Gen 22:2Gen 22:12Gen 22:16Jdg 11:34Pro 4:3Jer 6:26Amo 8:10Zec 12:10
1bsolitary, alone: the only one present, and so lonely
Psa 25:16Psa 68:6(7)
1cmy only one: a person's own life, named as the single life they have
It names the only one of its kind, with no sibling or replacement. It is the word for an only child, where the point is not how many there are but that there is no other.Gen 22:2Jdg 11:34
Because an only child is irreplaceable, it carries the warmth of precious or dearly loved, and its loss is the sharpest grief, the model for the deepest mourning.Jer 6:26Amo 8:10Zec 12:10
Turned on a person, it means solitary, alone, and forsaken: cut off from company rather than counted among others.Psa 25:16Psa 68:6
Of one's own life it means the precious, irreplaceable self, the single life a person cannot get back, used in pleading for rescue.Psa 22:20Psa 35:17
Both
Both can describe a single individual, and they meet exactly at Genesis 22:2, where God says to take your one and only son: the counting word marks the single son, while the only word marks that there is no other like him.Gen 22:2
It is the ordinary number one: counting a single item out of many, or marking the first in a series. This is its everyday job and the bulk of its uses.Gen 1:5Gen 41:25
It can mean a unity made of parts: many things counted as a single whole. Two people become one body, a divided people becomes one nation, and the Lord is declared one.Gen 2:24Deu 6:4Zec 14:9
It serves as the indefinite a certain one or any one, picking out an unspecified single member of a group rather than stressing that it stands alone.1Sa 1:1Ecc 4:9
Names an only child, the single son or daughter a parent has and could never replace.Gen 22:2Jdg 11:34Pro 4:3
Supplies the Bible's standard measure of the deepest grief there is, the way a parent mourns for an only son.Jer 6:26Amo 8:10Zec 12:10
Can stand for a person's own life as the one irreplaceable thing they have, so a prayer for rescue asks God to save "my only one".Psa 22:20Psa 35:17
Both
Both can describe a person left with no one beside them, and both treat that loneliness as a hardship crying out for relief rather than a peaceful solitude.Psa 102:7Psa 25:16Psa 68:6
Pictures a creature cut off from its own kind, so it reaches for images from the animal world: a wild donkey that has wandered off by itself. The other word is never used of an animal.Hos 8:9
Can describe someone straggling out of a moving column, one soldier no longer keeping his place among the ranks.Isa 14:31
oneness of a group, many people or things acting jointly or gathered as oneGen 22:6Psa 133:1
can also mean at the same time or all alike, marking simultaneity or completenessPsa 4:8Psa 14:3
yaḥid in the other biblical languages
μονογενήςGreek“unique”the Greek "one and only" or "only-begotten" that Genesis 22's "only son" fed into, applied to an only child and then to Christ as the Father's unique Son
Names a person who is alone and desolate, solitary rather than an only child: the sufferer with no one beside him, or the lonely whom God settles into a family.Psa 25:16Psa 68:6
Stands for one's own single, irreplaceable life, the precious self that cannot be replaced if it is lost. The psalmist begs God to rescue his one and only life from danger.Psa 22:20Psa 35:17
Both
Both name the sole and beloved child, the one child a parent has. The New Testament makes the link explicit when it calls Isaac Abraham's only son, the very phrase the Hebrew uses of Isaac in the story of the offering.Heb 11:17Gen 22:2
Both mark the only child as the one whose loss brings the deepest grief. Mourning for an only son becomes the picture of bitterest sorrow, and the widow's only son carried out dead is the sharpest form of loss.Luk 7:12Amo 8:10
Carries the sense one of a kind, the single unique instance of its kind, not merely a sole offspring. This is what lets it name Jesus as God's one and only Son, a use with no Hebrew counterpart in this pair.Jhn 1:14Jhn 1:181Jn 4:9
Becomes the flagship word for God's gift of his own Son: the Father sends his only Son so that those who trust him are not lost, a saving-love statement built on the word's uniqueness.Jhn 3:16Jhn 3:18
What scholars say about yaḥid
The lexicons treat this as a single adjective meaning "only, sole" with three contextual applications: an only child (Gen 22, Judg 11:34,Prov 4:3, and the mourning similes of Jer 6:26,Amos 8:10,Zech 12:10), the solitary or lonely person (Ps 25:16;Ps 68:6, where the plural denotes the isolated), and a figurative use for the נפש as the one precious life (Ps 22:20; 35:17). BDB and HALOT organize the entry along these lines, and TDOT notes the affective weight of the only-child sense that made Genesis 22 a locus for later theology. In the Septuagint the Genesis 22 phrase was rendered ἀγαπητός "beloved," while Aquila and later usage moved toward μονογενής "only-begotten, one and only," the term that carries the idea into New Testament Christology.
Sources
HALOT, s.v. יָחִידlexicon
BDB, s.v. יָחִידlexicon
G. J. Botterweck, "יָחִיד yāḥîḏ," in TDOT, vol. 6theological-dictionary