The Spanish ayudar, for “to help” is a close cousin of the English, aid. You can see that if we remember that the ‑y- sound is very similar to the ‑i- and thus the a‑y-d of ayudar maps to the a‑i-d of aid.
Both come from the same root: the Latin prefix ad- (“to”) and the verb juvare (“to help”). We can see the j to y transition here as well. Thus, both words are related to adjutant as well.