[all and one.]

1. Single; solitary; without the presence of another; applied to a person or thing.

It is not good that man should be alone. Genesis 2:18.

[This adjective follows its noun.]

2. It is applied to two or more persons or things, when separate from others, in a place or condition by themselves; without company.

And when they were alone, he expounded all things to his disciples. Mark 4:34.

3. Only.

Thou whose name alone is Jehovah. Psalm 83:18.

This sense at first appears to be adverbial, but really is not; whose name single, solitary, without another, is Jehovah.

To let alone is to suffer to rest; to forbear molesting or meddling with; to suffer to remain in its present state. Alone, in this phrase, is an adjective, the word to which it refers being omitted; let me alone; let them alone; let it alone; that is, suffer it to be unmolested, or to remain as it is, or let it remain by itself.