Having resemblance or similitude; similar; without difference.
"The twins looked so alike that it was difficult to tell them apart."
In plain English: Alike means being very similar to each other so that you can hardly tell them apart.
"The twins look so alike that people often mistake them for each other."
Usage: Use alike as an adjective to describe two things that are very similar, such as "the twins look alike." It is often confused with similarly when comparing more than one pair of items, but alike works best for direct comparisons between specific subjects.
In the same manner, form, or degree; in common; equally.
"The twins looked so alike that it was impossible to tell which one was older."
In plain English: When two things are alike, they share the same qualities and look or act very much the same way.
"The twins look so alike that people often confuse them."
The word alike evolved in Middle English by blending earlier native terms with a borrowing from Old Norse that meant "similar." This combination created the modern adjective we use today to describe things that are equal or very much like one another.