When filing for a Federal trademark, it's important to keep the SAM rule in mind.
SAM's not a person but a concept employed by the USPTO during their review process of new Federal trademark applications.
The USPTO will refuse registration "if the marks are similar and the goods and or services related." So basically marks do not need to be exact conflicts to be considered for refusal. ""Similarity in sound, appearance, or meaning may be sufficient to support a finding of likelihood of confusion," hence the SAM rule.
Let's take some time to dissect the third one – MEANING
Similarities in meaning takes into consideration that consumers could easily assume that marks that share a similar meaning are related, such as an offshoot product line or a new facet of a service. Because of that the USPTO will take into consideration marks that MEAN the same as one another.
Let's look at an example to illustrate this point.
You have a web site development service that you plan to name WebWorks & would like a Federal trademark. The comprehensive research you ordered showed a registered trademark for web site development for Internet Works. The words are different but for the average consumer the words web and internet are interchangeable and therefore are thought to MEAN the same thing.
*Comprehensive research will be on the lookout for SAM*