straightness, and so honesty: a motive with nothing bent in it, a life or road that runs direct rather than crooked, and what is simply right or owed
Hebrew builds one of its words for honesty out of a picture from the road. The root behind yosher describes whatever runs straight: a level route, a line with no bend in it. The noun keeps that picture and carries it in four directions, and Hebrew slides between them without reaching for a different word.
The largest group of uses is inward. Five times yosher turns up in the phrase "uprightness of heart": Moses telling Israel the land is no payment for their honest motives, Solomon remembering how his father walked before God, a giver insisting he has kept nothing back, a worshipper thanking God with nothing held in reserve. What is in view there is not conduct anyone can watch but whether the motive underneath it is bent. This is where the word stands closest to תֹּם, "integrity," with which it is twice paired, though that word pictures a person as whole and undivided while yosher pictures the motive as straight.
Two smaller groups stay nearer the surface picture: the settled uprightness of someone who actually lives that way, and the road itself, the "paths of uprightness" that Proverbs sets against ways of darkness. The adjective from the same root, יָשָׁר, "upright," does most of the work of calling a person or a route straight; yosher is that straightness treated as a quality in its own right.
The fourth use is the one English usually hides, because translations swap the noun for an adjective or drop it altogether. In a handful of places yosher means nothing more than what is right, fitting, or owed: honest words in Job, honest writing in Ecclesiastes, and, in two difficult lines of Proverbs, withholding from someone or striking someone contrary to what that person is due.