Every letter of the English alphabet has a "letter name". Vowel names are the same as the letters they represent, consonant names are usually <consonant>EE (e.g. B = BEE, C = CEE) or E<consonant> (e.g. F = EF, M = EM).
Though a letter naming standard exists, its practical usage in the real world is limited to scenarios like saying the alphabet aloud, answering queries of the form "how do you spell PHNOM PENH", or creating rhymes/songs. In the cryptic world, on the other hand, the possibilities of letter name usage are rich.
Letter names like BEE (B) and GEE (G) are also dictionary words with other independent meanings, and can be used on a clue's surface with interesting results.
Guardian 24893 (Pasquale): Alert old maid, possibly as bee-keeper (9) OBSERVANT
O (old) SERVANT (maid), keeping i.e. containing B (bee)
Letter names can provide wordplay options that the simple letter would not.
Guardian 25704 (Puck): Leading lady's letter to the papers (7) EMPRESS
EM (letter M) PRESS (the papers)
Guardian 26076 (Arachne): Wrongly use double ef in "defiled" (8) BEFOULED
The longer ones can be used for grid fill.Times Cryptic 4524 (Dean Mayer): Start to write the letter (3) WYE
W[rite] YE (the)
Sometimes, an unusual clue comes along with the letter on the surface and its name in the answer.
Guardian 26240 (Qaos): Writer who claims S, perhaps, equals T? (8) ESSAYIST
ES (letter S) + SAY (perhaps) + IS T
The Letter Name Reference Table
A reference list of names for all the letters of the English alphabet, from the Chambers dictionary
A closely matching list from the OED is on Wikipedia.
1. A wise crossword setter would use letter name substitution sparingly, as this device can easily slip into charade overdose territory.
2. If you've wondered why there isn't consistency in the naming of consonants (why should D = DEE and not ED, or M = EM and not MEE?), the reason can be traced back to Latin letter naming system, in which stop consonants were named <consonant>EE, sonorants and fricatives took the form E<consonant>. This link offers more insights.
Guardian 25900 (Philistine): A desire or aspiration (5)
Times 23937: Disney character after rest moved casually (7)
Times Club Monthly 20145: Innocent follower of ex (X) in action? (4-4)
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