What technique is used when comparing two things without using "like" or "as"?

The technique being described is a metaphor. A metaphor directly compares two things by stating one thing is another, rather than using "like" or "as," which distinguishes it from a simile. For example, saying "Time is a thief" does not just imply that time is similar to a thief but rather asserts that time takes away moments as a thief would take possessions. Metaphors create a more powerful and vivid image in the reader's mind by suggesting a deeper connection between the two compared elements. This ability to evoke imagery and emotion is a hallmark of effective writing, making metaphors a commonly used literary device.