1.verb(of separate elements) To join into a single mass or whole.
"The droplets coalesced into a puddle."
2.verb(of a whole or a unit) To form from different pieces or elements.
"The puddle coalesced from the droplets as they ran together."
3.verbTo 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.