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Hand in hand
Closely Associated
Use 'hand in hand' to emphasize strong connections between two things, often things that influence each other. 
Common Pairings
Some words are commonly paired with 'hand in hand' to form collocations; identify these to enrich vocabulary. 
Avoid Literal Use
'Hand in hand' is metaphorical when used to mean 'together'; don't confuse it with its literal holding hands meaning. 