Attain means to succeed in achieving something or to reach a specified size or amount. Attain implies an effort to achieve, while obtain is to gain possession of something. However, in everyday usage both attain and obtain are often treated as synonyms.

Assumption means to accept something as true which isn’t founded on strong evidence, while presumption is based on evidence which has some credibility.

Assent indicates the approval of something after careful consideration, while consent implies something is being allowed. For consent, the consenter may not necessarily be happy about the outcome.

Assemblage tends to be an informal collection while assembly refers to a more formalised group, such as a national assembly or school assembly.

For a general audience, assault and battery have the same meaning. While this may vary depending on your country of residence, typically battery involves physically touching someone, while assault doesn’t and instead refers to the threat of violence. In some jurisdictions, this distinction between assault and battery no longer applies.

Apt means suitable in a given circumstance, have the tendency to do something or be quick to learn while likely means probable or promising.

Approve means to accept something as satisfactory while endorse means to declare public approval or support for something. While approve implies that the approver has a positive attitude towards something, endorse implies a positive attitude and active support.

Apprised means to assess the value of something while apprise means to notify someone about something.

Any place means any location while anyplace is an informal usage of anywhere. Anyplace is often used in spoken language and using it in writing is considered non-standard usage. You can use anyplace in creative writing, but it’s best to use anywhere for official or formal writing.

Anywhere means in, to or at any place and can be used to indicate an indefinite location, while any place has a narrower meaning of any location.

Anyway means regardless and shows a disregard for things that may stop someone from taking a certain action, while any way means in any manner or however possible.

Both anyway and anyways have the same meaning of regardless or in any case, but anyways is more informal. It’s fine to use both in your writing but I recommend you tailor their usage to your characters’ speech patterns and personalities.

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).