Letter a problem, initially dropped? (5)
I believe the answer is:
aitch
'letter' is the definition.
(aitch is a kind of letter of the alphabet)
'a problem initially dropped?' is the wordplay.
'problem' becomes 'hitch' (I've seen this before).
'initially dropped?' means to remove the first letter.
'hitch' with its initial letter taken away is 'itch'.
'a'+'itch'='AITCH'
(Other definitions for aitch that I've seen before include "character leading heroes" , "Aspirated letter" , "It's dropped by Cockneys" , "that may be dropped" , "bone" .)