If event A must occur for event B to occur, then it is said that
A is → necessary for B. If event
A may cause B but there could be some other cause as well, then it is
said that A is sufficient to cause B. See also
→ if and only if (iff).

1) Adequate for the purpose; enough.
2) Logic, Math.: A condition which, if true, guarantees that a result
is also true. However, the result may also be true if the condition is not met.
→ if and only if.

M.E., from O.Fr. sufficient, from L. sufficiens, pr.p. of
sufficere "supply, suffice," from sub "up to,"
→ sub-, + root of facere "to make,"
→ fact.

Basandé "sufficient, complete, worthy," from *basidan, from
bas "many, much," → multi-.