Incorrect spelling


Incorrect spelling, explanation: this form is incorrect because the origins of the word are in Middle English atachen, so with just ch, not tch. /tʃ / sound is sometimes connected with tch, but sometimes also with ch, so this can’t be taken as a rule. Therefore attach is the correct form, and attatch is incorrect.

Correct spelling


Correct spelling, explanation: attach is the correct spelling, due to its Middle English origin: atachen. Attatch is a mistake and this may be due to the fact that many second language speakers consider /tʃ / sound as tch, this is however not the rule. In this case, it is ch, so attach is the only correct form.

Definition of attach:
verb, to include or annex something
Could you attach the mobile phone number to the business card? It is needed there.
I usually attach this spreadsheet at the end-of-the-month report.