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So don't worry so much about how to use  had had  as a unit of grammar, they will come together naturally when you want to express the verb ' to have ' in the past perfect. Let's consider a different verb for a moment like  to want .
âsynergyâ: synonyms and related words: 1  accompanying. 2  accord. 3  allied. 4  ally. 5  along. 6  alongside. 7  as one man idiom. 8  bosom. 9  en masse. 10  formation. 11  gang. 12  gang up. 13  hand in glove idiom. 14  joint. 15  partnership. 16  put sth together. 17  put their heads together idiom. 18  stand together. 19  swarm. 20  tandem.