From yachad; properly, united, i.e. Sole; by implication, beloved; also lonely; (feminine) the life (as not to be replaced) -- darling, desolate, only (child, son), solitary.
see HEBREW yachad
H3173. yachid
יָחִיד adjective and substantive only, only one, solitary (Late Hebrew id.; Aramaic יְחִידַי יָחִיד,, , , id.; Arabic solitary) —
1 only one, especially of an only son, Genesis 22:2, 12, 16 יְחִידְךָ את בנך את thy son, thine only one, יָחִיד אֵבֶל Amos 8:10; Jeremiah 6:26 mourning for an only son, היחיד על כמספד Zechariah 12:10; Proverbs 4:3 אמי לפני וְיָחִיד רַךְ; so feminine יְחִידָה Judges 11:34.
2 feminine יְחִידָה as substantive Psalm 22:21; 35:17 יְחִידָתִי my only one, poetic for my life, as the one unique and priceless possession which can never be replaced (in each "" נַפְשִׁי).
3 solitary, Psalm 25:16 אני ועני יחיד כי; 68:7 בַּיְתָה יְחִידִים מוֺשִׁיב causing solitary, isolated ones (i.e. friendless wanderers or exiles; "" אֲסִירִים) to dwell at home (Lag Ch and others מֵשִׁיב bringing back home).