A masculine hand you don't recognize comes into contact with yours. It may be large, marked, calloused, smooth, loving or indifferent.
The emotional tone
A mix of curiosity and reserve. Sometimes attraction, sometimes simple attentive neutrality.
Symbolic meaning
The unknown masculine hand represents the structuring part of oneself, what Jung called the animus in women, or the otherness in men. It figures a force of action seeking to present itself.
The palmistry link
In palmistry, a wide and firm hand refers to the mount of Jupiter and the fate line. Dreaming of an unknown man's hand is often dreaming of an inner authority seeking recognition.
What this dream signals in your life
This dream arrives when a structuring decision must be made. It doesn't designate an outside person: it names an available inner resource.
The unknown in the dream already knows you. They're a facet of you waiting to be greeted.