Noun. Also ache (obsolete). Mid-16th cenutry.
[Old French ache, perhaps from Proto-Romance word exemplifying the sound.]
The letter H, h.
Aitch, bless it, is one of the more controversial letters in the English language, and people can become very passionate about whether it's pronounced with an initial h sound or not (as in haitch rather than aitch), and it's often very much looked down upon in accents and speech patterns that drop the aitches, as in meeting someone that says they're from 'erefordshire rather than Herefordshire. Personally, I don't give a fricative. What really bugs me is when people don't believe that letters have spellings too, usually manifested during a game of Scrabble when they challenge a word like aitch or ess or any other such letter. Grrr. Drives me mental it does. Such people should be banned from playing Scrabble. For life. And be forced to to wear a placard that says 'I Challenged Aitch in a Game of Scrabble.'