Anyone references no person in particular while any one refers to a single person which makes up a group. If you are unsure which version to use, if you can replace the word with “any”, then you would use any one instead of anyone.

Both amount and number mean quantity or amount. Amount is used with mass nouns (small, large) while number is used with count nouns (five, those).

Both amiable and amicable mean friendly, but amiable refers to people while amicable references relationships.

Altogether means completely or totally, while all together references unity of time or place.

Amend refers to making minor changes, while emend means to remove mistakes from something, such as a text.

Alternate and alternative as nouns have the same meaning. Alternate is more popular in North America while you’re more likely to find alternative used in UK English.

Altar refers to a table used in religious ceremonies while alter is a verb meaning change in character or composition.

All ready refers to preparation while already refers to time.