or add, esp. to something larger or more important:annexed a building to their headquarters.
To take control of (territory) from another country, often by force: Germany annexed Czechoslovakia.
Although annex an attach can be similar, I would say the usage of the latter is significantly more frequent. The word "annex" is more formal, common in books, specially titles or indexes.
See more uses of annex below:Annex
) to take control of a country, region, etc.
Germany annexed Austria in 1938.
The territory had been annexed to Poland.
(annex is very common in this context
from: WordReference Dictionary
1. To append or attach
, especially to a larger or more significant thing
2. To incorporate (territory) into an existing political unit such as a country, state, county, or city.
3. To add or attach, as an attribute, condition, or consequence.
from: The Free DictionaryAttach
you can use in everyday conversation without being too formal.Fasten/join
: He made certain that the trailer was securely attached to the van.Fasten
(a related document
) to another, or to an email
I attach a copy of the memo for your informationInclude
(a condition) as part of an agreement:
The Commission can attach appropriate conditions to the operation of the agreement.Attach oneself - to Join (someone or something)
Without being invited: they were all too ready to attach themselves to you for the whole day.
from: Oxford Learner's Dictionary.
I hope it can help a little bit...