The following reaction is an example of

$\mathit{CaO}\left(s\right)+H_{2}O\left(l\right)\to \mathit{Ca}\left(\mathit{OH}{)}_2\right(\mathit{aq})$

The following reaction is an example of a combination reaction.

In a reaction when two or more reactants combine to form a single product, the reaction is called a combination reaction.  It is generally written as
$X+Y\to \mathit{ XY}$

Combination reactions are also called synthesis reactions.

Calcium oxide which is commonly called quicklime reacts with water, and calcium hydroxide which is commonly known as slaked lime is formed as CaO combines with water to form calcium hydroxide.
$\mathit{CaO}\left(s\right)+H_{2}O\left(l\right) \to \mathit{ Ca}\left(\mathit{OH}{)}_2\right(\mathit{aq})$

During this reaction, heat is produced when a product is formed so it is also an exothermic reaction.

Hence, the reaction shows both a combination and an exothermic reaction.