Equally or mutually constrained or restricted; confined together.
From the prefix 'co-' (together) and 'straight' (narrow, constrained), with roots in Old English and French. This archaic term combines the concept of mutual restriction or shared confinement, though it has largely fallen out of use.
This word is so old and obscure it barely exists in modern English anymore, but it's a perfect example of how 'co-' can make words mean 'together'—costraight would mean you and someone else are stuck being straight or narrow together.
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