(of separate elements) To join into a single mass or whole.

(of a whole or a unit) To form from different pieces or elements.

(engineering) To bond pieces of metal into a continuous whole by liquefying parts of each piece, bringing the liquids into contact, and allowing the combined liquid to solidify.

(of separate groups or persons) To merge, to intermingle freely.

(databases, SQL) To convert a null value to a defined value.