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tip of the tongue phenomenon

A psychological condition in which a person cannot recall a specific word or term but has a strong sensation of knowing it, often able to recall details such as the first letter.

Examples:

I was experiencing the tip of the tongue phenomenon when I needed to remember my friend's name at the party.
Despite knowing the word was on the tip of my tongue, I couldn't articulate it during the discussion.

retrieval failure

A memory phenomenon that occurs when a person is unable to access information stored in memory, often evidenced by knowing certain details like the initial letter or other associations with the word.

Examples:

Retrieval failure can be frustrating, especially when you have an important meeting and forget a key term.
When faced with retrieval failure, many people try to think of related words to trigger the memory.

frontal lobe activation

The engagement of the frontal lobe of the brain, involved in recalling memories and language processing, which can lead to situations where one remembers the first letter but not the full word.

Examples:

Frontal lobe activation is crucial during language tasks, which explains why I remembered the initial letter but not the word itself.
Research on memory retrieval often examines how frontal lobe activation contributes to experiences similar to the one where you just recall the first letter.