Block letter and Letter of the alphabet

Block letter noun - A plain hand-drawn letter.

Letter of the alphabet and block letter are semantically related. In some cases you can use "Letter of the alphabet" instead a noun phrase "Block letter".

Letter of the alphabet noun - The conventional characters of the alphabet used to represent speech.

Block letter and letter of the alphabet are semantically related. Sometimes you can replace phrase "Block letter" with "Letter of the alphabet", this phrases are similar.